*Vibes for an easy spay and quick recovery*
You’ll want to have a clean cage to bring her home to, keep it clean; Have treats ready (like her favorite greens) to keep her eating. Try to limit her movement (don’t let her play out of the cage probably for two days). Keep the environment warm and quiet so she can rest.
Do not leave the vets office without pain meds; Many will try to send you home without them; Just put your foot down and don’t leave without something like metacam. Spays are fairly invasive and they should get a couple of days of help with pain.
If you want to be really prepared, pick up some critical care (usually the vets office sells it) and if you don’t have all night grocery stores or pharmacies (in case it happens at night) pick up some pedialyte and baby food and syringes incase you have to syringe feed and water.
Likely it will all go very smoothly but it makes you feel better to be prepared!