Good luck with Brandy's spay tomorrow, she will do just great.
When Maggie was spayed, they sent me home with some pain meds. We wound up giving her one dose that night and she was okay the next morning, just a little bit quiet. You'll want to keep her quiet for sure for the first few days. Once Brandy starts to feel a bit better, it will probably be hard to keep her from running around and jumping, but you definitely want to be calm.
I put a onesie on Maggie and she peed right thru it before I could get to her. lol. It certainly didn't hurt anything, I just changed her into another. I have soft cone collars called the Kiss-E Collar, if you should decide you want to try one of them for Brandy. Best of luck and let us know how she does.