I honestly don't see how she'll manage to retire completely on just 300K. If she sold the house for maybe 200K profit to her once her loans are paid off, maybe she'd be able to squeak by tho. Doing a 4% SWR, if she had 500K invested, she'd get 20K a year until she got SS, so she would definitely need to stick to a budget and be careful about frivolous expenditures.
So big thing is figuring out her current spending, and setting up a budget.
Instead of buying a small condo, she might want to consider selling the current house and finding a nice (and less expensive) apartment to rent - maybe closer to where you live so you can help her out? Then she doesn't have to worry about property taxes, homeowners insurance (but check out renter's insurance), maintenance and repairs, and she'll be near family so you can touch base with her much more often to make sure she's okay. She also might be able to downsize her furniture and other stuff and make a little profit depending on if she's got anything nice to sell. A smaller place also means she should be paying less in monthly utilities as well.
I'd also help her do some research on disability benefits that might help out (if she is unable to work at all) until she hits SS age.
I'd definitely roll her over to Vanguard or even Fidelity. (I love their website and they have great customer service, and as long as you're staying in their low expense funds like the Spartan series, they are VERY competitive with Vanguard). I know I actually manage my husband's IRAs - he knows how to log in and look at them, but he lets me figure out what to put it in and move it around... as long as she is comfortable with you dealing with that part, you could just manage her account for her and make the investments and transfer money to her bank account when she requests it.
As far as the portfolio setup, I am still a noob at all of that, so take whatever I'm suggesting with a VERY large grain of salt, but I remember reading about Vanguard's Wellington Fund on one or two other blogger sites as the fund they're going all in on when they're in retirement. It is a balanced mix slightly weighted towards stocks, but a really good fund that should weather the ups and downs well for someone with a long-term retirement. But it would be a bit more of a bumpy ride and not as conservative as mostly bonds (the mix is like 65% stocks, 33% bonds and the rest in short term/cash). Maybe not as the total holdings in her investment account, but could make up a large portion of it and then get some straight-up bonds for the rest. It does say that the Wellington Fund is tilted towards dividend-paying stocks of established companies along with income-producing bonds - so this would be a decent fund to just go all in on if you're not wanting to have to actively rebalance.
https://personal.vanguard.com/us/funds/snapshot?FundId=0521&FundIntExt=INT#tab=0And of course, there's you and your husband - how much help (money or otherwise) are you willing and able to give her? If she's able to get around 500K in a decent investment setup and cut her budget down to around $1500 a month (that's slightly under the SWR for an investment amount of 500K), could you help her out in the event that she has a financial emergency? Something else to think about.