When I got Belle and Delilah spayed, they stayed overnight. I don't think they ate anything. Apparently they are droggy the day of, and then I picked them up before 8am the next morning. I doubt they would have ate anything at the vets since they would have been stressed out. Might be worth taking a small amount of food with you and asking when you drop her off anyway!
I let them have free roam of the apartment when they got home (I was home with them). The first day I brought them home, they just rested and stuck to my like glue. They were pretty much back to normal the next day. I just kept a close eye on their wounds, which were much smaller than some I have seen here on TCS. I would suggest just keeping a close eye on her for the first few days. I let them climb up their cat tree so they could see out the window, etc, but I broke up "fights" when they started playing. Both healed fine.
It won't change her personality. If anything, I think mine have become bigger sucks since they had it done. They still get their spurts of kitten spunk, although I think something to do with hormones means that she may calm down a bit. In any case, the change in personality is NOTHING compared to what it is like when they go into heat. My poor, quiet little Delilah was just crying and crying when she went into heat (at 4 1/2 months)...and just moped around...I felt so bad for her....I drove right up to the vets to schedule their spay, so we didn't have to go through it again!
for Nora. I know I was a worry wart when the girls were in, but everything turned out just fine! Just give her some extra love before and after!