The price difference between cross country one-way legs and the same round trip is next to nil these days. Buy her a one-way, then buy the return 2-3 days before she's due to come back.

The other trick is that you can buy a ticket on a credit card then cancel it for free within 24 hours on almost any airline (this might be US law). You can keep reserving return tickets then cancelling if she needs to stay longer. I've done this for days in a row, literally. I think with American, you can even sometimes do this WITHOUT a credit card.

Per KAYAK.com, Pittsburgh to LAX via CLT is $175 one way (including tax) on American right now, leaving any day this week. Return price is the same. $350 is about as good as you'll get for a round trip. You might not even have to buy the ticket in advance, she can probably just go to the airport and buy it the day she wants to leave.

Good luck. Judging by the condition of the house, I wonder if your son's wife is into something she shouldn't be, like meth.