If you decide to leave her in a room make sure it is fairly puppy proofed, and you can always leave the crate in the room with the door off. She may like sleeping in it. The foster probably crated because they have their own pets and it's easier to separate them.
Sorry I have nothing nice to say about the fellow who's wife died and he ditched her dog for another ...... I'll leave it unsaid. I don't like her either. If my hubby told me to choose I'd pack his bags!!
I think your girl will do fine so long as she has some toys to keep herself busy. Try stuffing a kong with some low fat peanutbutter and freezing it and then giving it to her as a treat when you go out.
Make sure you walk her before you go out. A tired dog is a good dog. And just try her for a few short times first before leaving her full on by herself.