No, you need to be fitted in real life. Shoe fit varies between manufacturers. Not the overall size but heel and forefoot width as examples.
Look for a running shoe store locally. Avoid big box stores, they will try to fit you in whatever is on sale and seldom, if ever, carry real running shoes.
See if there’s a running club around, they should be glad to help.
Couldn’t she try and look at an outlet store or something, to save money?
Not the first time – she needs to be accurately measured and fitted for the right size. And take notes about which size fits you best in each brand, regardless of which one you buy.
After that, when she knows her size, she can go to an outlet store, big box store, or even online to purchase shoes.
Also, continue to avoid the pricey, fashionable gyms – they aren’t worth the money. But there are usually much cheaper ones available. Look into YMCA/YWCA facilities. Or public ones – don’t you have a park system in your town? And many public schools have nights where they are open to the public for free or low cost.
You might want to consider starting with swimming rather than running – good weight-loss exercise, without all the stress on your legs/feet. Many public schools with pools make them available at times.
Do some searches online for shoes that help severe over-pronation and that have motion control. Read the reviews and make sure that they will work for flat feet.
I usually look around online. Do my research on Zappos, then buy on either Amazon or Zappos, depending on price. Do not choose on looks. Choose by motion control and stability. You want maximum until you get much, much better at this and things stop hurting and twisting.
I hear you on the price, but if you’re in pain now, it’s going to get worse. Everything is driving down on each step to impact through your shoes.
Try walking instead of running until you’ve lost more weight, as one option. Walking has actually been shown to have really good long term effectiveness rates.
Swimming is also easier on your body. Check local public facilities, but don’t forget about the YMCA or the YWCA.
I’ve been where you are. One step (or stroke) at a time. You’ll make it.
Do gyms still offer ‘30 Days Free’ promos?
Whatever else, STOP RUNNING!
In San Francisco, it was/is common to see ‘home gym’ equipment on the curb (which means: I have no no further use for it, but you might be able to use it) after the initial "I’m going to get fit’ turns into the ‘damned thing taking up the living room’.
Check Craigslist under ‘Free Stuff’.
t-bonham–there are quite a few parks here and even a semi-nice trail system through the “woods” that adjoin a public park which I really quite like when I have the time to drive over there (it’s a 20 min drive) and walk it. 
It’s really quite pretty.
I’m going to check to see if our local high school gym is open nights, etc for free/low cost but that would only work if there’s also childcare of some sort. I have an 11 yr old with high functioning autism and we’re not quite at the point where we feel 100% comfortable leaving him alone at home for any length of time. Plus…at least until he’s 12…it’s sorta illegal in this state to leave him home alone.
usedtobe–they might, but getting to the nearest gym (which for me is a 24 fitness) would be a bit of a crunch.
Right now, as it stands…I have approximately an hour between the time I get off work and the time I need to go pick up my son, which is when I plan on doing my workouts. I can take clothes to work to change into and work out in the neighborhood near my school (I’m a school lunch lady) for about 30-45 min and then go to pick up my son at his school down the road.