Hi - best of luck on the spaying - I'm sure she will just fine
!
Before leaving the vet, *make sure* you have pain medication AND a pain plan for what you're supposed to do if/when it appears that the pain is not being managed enough -- the vet will have a plan for that, and you should know it ahead of time, always. Stay ahead of the pain by making sure you give pain meds on time.
Try to keep her quiet by giving lots of chew bones or chew toys or kongs etcetera.
You will be surprised how quickly she snaps back...but be prepared that the first night she may be groggy, foggy, seem low, quiet.
Let us know when she is out of surgery!!!