This bit about Metro does not seem to have been mentioned yet, so I will go ahead and do so.
On weekdays between opening and 9:30 and 15:00 and 19:00 peak fares are in effect. During the weekend peak fares are Midnight to closing. The difference in price can be almost double depending no how far you are travel. It might be wise to plan your wanderings about accordingly.
//i\
:dubious: How did she get the other adults in the party to go along with her?
Since the airports have been mentioned, let me make one point. There are three airports near D.C. The fact that BWI (Baltimore-Washington International) airport is called Baltimore on arrival/departure electronic boards in airports doesn’t mean that it’s not convenient to Washington. When you book a flight to the D.C. area, you should always check all three airports. I live ten miles from the center of D.C. and I nearly always fly to and from BWI. Sometimes it’s even cheapest when you’re going to a Virginia suburb, to fly to and from BWI, even counting the cost of a taxi getting to and from your destination. The Maryland suburbs have hotels too, incidentally.
I would book a Super Shuttle rather than a taxi for the trip from the distant airports.
Not just in the Metro system, but in all of life, really: when you go through a doorway, be it the Metro gate, the train doors, the elevator, or at the top or bottom of the escalator, DO NOT JUST STOP, KEEP MOVING. People won’t push you over, but they should.
I cannot tell you how many times I’ve gotten stuck behind a group of clueless tourists who think it’s perfectly fine to step off a moving platform full of people and just stop to get their bearings and debate their next move. Please just get out of the way. I promise you, you’ll still be lost two steps over to right.
SSSHHHHH! Keep them in Virginia! 
Be aware that most Metro stops have more than one exit, and the in-station signage is terrible. Much of the signage just says something like “North Side” or “East Side” or lists the intersection, information which is probably going to be meaningless to you. I live here and it’s mostly meaningless to me.
I’m telling you this because going out the wrong one will probably only cost you a block or two extra walk. It’s not really a big deal if you go out the “wrong” exit.
A valid alternative is to throw a fit instead, which is known to make the Metro employees eager to help you out.
If you aren’t driving and thus won’t have a car to park, I’d consider staying in the city. There are some affordable hotels in interesting neighborhoods. Personally, I find driving in the city much easier and less stressful than driving in the suburbs around the city, but it’s an issue of what you’re used to. The Tabard Inn is a great DC hotel that is pretty reasonably priced, https://www.tabardinn.com/.
If you do decide to drive into the city, and have a specific destination in mind, I’d recommend an app called “Parking Panda.” It’ll find you garages near where you want to go, and in most cases will get you a modest discount. You pay through the app, and your reservation includes detailed instructions for the garage (some have a QR code scanner, some have an attendant, some have some other system; read the instructions carefully). Also, note many garages in DC are clustered together, some with entrances right next to, or across the street from each other, so be sure you’re going into the correct garage.
It still won’t be cheap, like $10-20 or more (though I’ve gotten all-day parking for $5 before), but you’ll have a guaranteed space, in many cases all day, and you won’t have to worry about finding a space on the street, which during daylight hours in most places you’d want to go, is basically impossible.
About 3 years ago we visited and stayed out of town. We bought our Metro cards one morning, but coming back they didn’t work. Seems we’d gotten into peak time and we were stopped dead at the turnstile with people crawling up our backs. The attendant finally noticed and opened and way for us to get out of the way, extracted a bunch of $$$ from us and let us go. You won’t get much help from those attendants.
I really wouldn’t overthink the Metro SmarTrip cards. You see your balance every time you touch in or out and you can also check it at the fare machines. If you end up with a few extra dollars on the card, then keep it for a next trip or give it away. I’ve found one in my hotel room with a sticky note telling me there was $5 remaining.
The OP doesn’t make it clear if they’re flying into DC or driving there. If flying, I highly suggest Washington National Airport which has its own Metro station. As far as airports go, National is one of my favorites. It’s reasonable size and security seems to be efficient even during the government shutdown. Of course, it may be different in summer with more infrequent flyers. Food and drink are expensive and you’ll think you’re paying off the national debt after a couple drinks and a meal, but that’s not uncommon in most airports these days, especially on the East Coast.
Seems like a no-brainer to me for hotels in the area to offer SmarTrip cards with say, $15 preloaded as a room add-on. I’ve not yet heard of any hotels that do this, but then again I live in the area so I’ve never needed to stay in a hotel around here.
I honestly don’t know if they sell them at other places besides Metro stations. I bought mine at the Metro station at National airport because I needed it to get to the hotel. In Chicago, you can buy Ventra cards at CVS and Walgreens and other places. But, the CTA also takes Apple Pay and contactless cards. Hopefully Metro will do the same in the future.
What are you saying exactly? Are you suggesting that the attendant demanded a bribe? Or was it that your cards had insufficient funds for completing your trip and the attendant made you pay the difference?
Strangely enough, every problem I’ve had in the metro system has been solved by an attendant, and I don’t recall any rude behavior in such a situation.
Even when I have asked to use the restroom in a (personal) emergency situation, the vast majority of the time the attendant has let me do so. On a handful of occasions I’ve been told that the restroom is out of order (which is possible, I guess). But I’ve never been told “No, it’s not for public use.”
You can buy a smartrip card at some CVS and Giant stores in the DC area. Sales Locations | WMATA
Also the Commuter Stores.
Yellow will be down too south of the airport. So Alexandria is right out after late summer.
Philadelphia I have driven in, and I found Washington worse.
Thank you all for your comments and advice!
There are “Add Fare” machines inside the gates for just this eventuality - if you need money to exit, you can just add a bit there.
I suspect WMATA never saw any of the money the attendant extracted from you.