And then very visibly sit on your porch and drink a lemonade.
Why not just tell her that the first one was free but the rest will cost her gas and time spent along with possibly a meal if its a long haul. And then only if it works into your schedule. Then see how fast she will move on to the next free ride.
Just be straight up about it and see where it goes. If you decide to settle for less than I suggest then fine, it’s really all up to you. Do you mind being with her?
Next time they call, say you can’t take her but you’re willing to show her how to set up Uber/Lyft on her phone.
Thank you all for your replies, even the ones who called me a door mat and the like. I know I have tendencies that way, my mother always stressed me being helpful and friendly to everyone and I guess I internalized it too well. 
In somewhat my defense, most of Mary’s requests have really not been burdensome, individually speaking. Like the hair salon she uses is in the same strip shopping center as my preferred grocery. So, she had an appointment for Thursday at 2 p.m.? Well, fine, so I just got my shopping list ready a day earlier than normal, dropped her in front of her shop, parked a few stores further down the row and spent the time doing something I’d do normally. Such a trivial change on my actions it’d be silly to call it even an inconvenience.
And many other stops she needed were in town and she expressed them as ‘sometime this week I need to visit’ some place, so again, not a hassle to combine them with errands I’d be doing anyway. It was just that it happened too often.
What was mainly annoying were the ones to out of town places, and especially ones far enough away I’d just have to sit and wait for her to be done or because it made no sense to go and come back a second time to bring her home.
And of course yesterday I was very NOT happy about losing three full hours when I’d thought it would only take an hour or so… and felt very abused. I’ve calmed down a lot over night.
And the idea that maybe she does have a problem she’s trying to hide is a good point. My mother had Alzheimer’s. For some years before it was obvious there was a problem she’d started avoided driving on highways. She’d said she liked to ‘see the scenery’ and ‘enjoy the quiet’ so she preferred to take backroads even if they took longer. Looking back, we realized it was a coping mechanism for her, that she was finding highways too stressful and challenging. Mary’s only in her 50s where my mom was mid 70s when this started, but the timeline varies or it something else but similar.
So. Maybe I won’t cut her off completely. Maybe I’ll just tell her I can only give her rides within town, and she’ll have to figure out other arrangements for anything farther/longer.
(No, I don’t dislike being around her. We were never really friends, just casual acquaintances, but we can chitchat about stuff for short spans with no problem.)
Came here to say the same, but I’m not kidding. Enforcing that rule (other than the occasional rare request from fam/friends/neighbor) prevents these unfortunate and uncomfortable situations.
Ah, so you don’t mind being used?
How much do you care about this person?
How about next time, you tell her that you’re going to be at the grocery store at whatever time you’ve planned and she should plan her hair appointment around that?
Another possibility – if [lots of things] worked out and were okay with you: use one of their cars to run her around.
It might make it much easier for you to say the car needs gas, and for her to get the clue … that … paying for gas for her own car is her responsibility.
The upside there is that you’re “only” donating your time.
Obviously I don’t know the whole situation, but I think you could be setting yourself up for being manipulated in ways that are just more subtle and possibly more annoying - like you give her a ride in town and it turns into something else when you’re halfway there.
Same thing with making excuses - if I’m reading the situation correctly, the person using you already knows how to navigate around any slight reluctance or reasonable-ness you display. You’re trying to be nice (which is admirable) to a person who is already exploiting your niceness.
This very much reminds me of my mom’s situation when my dad passed away, she lived alone for almost 20 years and was able to drive herself much of that time. She helped friends with rides for many years while she could and when she no longer could drive, she asked her few remaining friends, family and acquaintances to help get her to appointments. The town she lives in is only about 20K people and no taxi or Uber service, as she is about 35 miles northwest of Dayton Ohio in the middle of cornfields. The county has a shuttle service for hospital and doctor appointments, but it’s a huge pain for older people to use due to waiting periods.
Two years ago during Covid, it looked like I was going to need to put her in a nursing home because all her friends and acquaintances had died or were no longer driving themselves. Not a good option during Covid. As luck would have my brother wanted to move out of California due to the wild fires and issues with the smoke in the air and was able to move home to be with my mom. He is retired and has diabetic issues (missing one leg) but was able to figure out how to get groceries delivered and found out the town finally got door dash (still no Uber).
So to cut to my point, perhaps she isn’t so much mooching rides off of you as she is trying to remain independent for as long as possible. She may just be scared.
But she refuses to offer payment? She’s mooching.
I suppose it’s marginally possible she’s not mooching, but is just innocently impervious to subtle hints about paying for fuel etc. That’s why I think a direct discussion of the situation is probably worth having.
You (StarvingbutStrong) say that you know that you’re allowing her to use you, so I won’t say it.
But you are also being ridiculously passive-nonagressive by hinting that you want gas money without coming right out and telling her you want gas money. You need to stop playing these games. You’re a grown-up. You’re not helpless. You have agency.
If you do decide to take her phone calls again, tell her that unless you’re already going wherever it is that she wants a ride to, you aren’t going to take on the job. And that she will also have to start paying for gas. You don’t have to offer her any other explanation, she knows perfectly well that she’s been taking full advantage of you. If she then forgets the gas money (which she most likely will), then cut her off.
If you’re concerned that she’s hiding her inability to drive herself anymore, than she can say so. She can sell one of her cars that she can’t drive and help pay for her rides - it’s not like she needs to paying insurance on a car she can’t drive.
Remember, nobody can use you as a doormat without you lying down on the ground first.
She is totally in the wrong to be so presumptuous as to treat you as her free taxi service. Only if she was a close relative would she have any justification. You would be totally in your rights to cut her off completely. If you continue to have a relationship with her, be sure to maintain strong boundaries. I would not be surprised if she also wants you to be her free personal shopper, free landscaper, free cook, etc. Don’t even start to go down those paths. She’s an unashamed taker and will drain you of everything you can give.
If you continue to give her rides, don’t make it so convenient. If she wants to go shopping Tuesday at 2, tell her you wouldn’t be available until Thursday at 8. If she wants to spend 2 hours shopping, tell her you have to be back in an hour. Don’t make it so easy for her to have everything work out her way. Maybe the hassle will cause her to drive herself or find someone else to latch on to. If you need an excuse, say you have taken up online backgammon and you have games scheduled. Or say your friends on the SDMB miss you too much when you’re gone 
A moment to give the OP kudos for being a good neighbour. It’s hard to draw the line sometimes: think “frog in water slowly warming to the fatal boiling point.” But you’ve reached that line, and it’s good you have. And more kudos for being reluctant to simply give Mary the old heave-ho. You don’t have to give her ultimatums or ignore her or respond with the righteousness indignation of a wrathful god. When she calls and makes her request, you can simply decide whether you want to take her on this particular trip and say, “I’d love to,” or “I’m sorry, I can’t.” Either way, you know she is not going to bake a cake or pay for gas, and you can decide if you want to bestow an act of kindness that will not be reciprocated. The key might be to remember you can make the choice and whatever you choose is okay and decent, as long as you don’t do it from anger (however justified your anger is!)
My husband drove a neighbor around for a year or two. She was an old lady who didn’t have a driver’s license, but she was similarly a moocher. I guess she gave me a large ceramic pot, once. (My husband did all the work.) After mentioning it to a neighbor, he learned that he was the fourth neighbor she’d used that way, the lady next door had done it before he did.
Various people (like my husband) suggested she hire a cab, or get groceries delivered, or… But she liked the outing, and admittedly, that was before the days of ride-share and cab service was unreliable.
I think a breaking point was when he got a ticket for “parking” in a handicapped spot when he pulled into it to let her out. And she didn’t do boo, not even apologize, let alone offer to pay for the ticket.
Eventually he told her he couldn’t do it any more. I have no idea what she did after that. She didn’t die of starvation, though.
Yes, Mary will find another ride. Trust me.
OTOH. I’m not safe to drive myself at the moment. My family would never say no to me. I really hated using them so much. They do alot already and are very busy people.
We took a step and hired me a helper, CNA, companion, bossy jerk to do for me. It’s very expensive. I feel worth the cost. Except the days I wanna kill the woman in her sleep, 
.
Not everyone can do this, I know. Why can’t she hire someone to drive her in her car? Maybe a safe older teenager. I can imagine that would be an easy job to fill. And not very expensive.
Suggest it to Mary.
Your situation is why we work hard at trying to establish and maintain what we call, “Hey neighbor” relationships, resisting most efforts at anything closer. It is all too common that a good deed or social invite here, or a perceived insult there makes your neighbor situation something you have to deal with. Rather than just someone you wave to and say, Hay, neighbor!" when you see them.
Yeah, no question neighbor is a user. And it is understandable how you let an initial good deed snowball. You created this situation. Only you can decide how to stop it/scale it back. I’d probably just find the balls to say, “Driving you just doesn’t work for me anymore.” Period, full stop. She can make whatever arrangements she wishes.
Trying to drive her sometimes and not others would be - for me - an undesirable ongoing negotiation/hassle. Unless she is destitute, it isn’t as though taxis/Uber are unheard of.
Also if you give her rides, do so in her car. Say you’re worried about expenses and are trying to save the wear and tear on your car. If her car needs gas, use her card to pay for it.