I understand your worry! My Shadow bun was spayed 1 week ago and I was very concerned about how it would go (fortunately all went well!).
I learned a few things from having my somewhat nervous boy neutered 6 weeks ago. He spent 4 hours in his carrier waiting for his surgery, and was too scared to eat or drink. This continued after surgery so he became dehydrated ect. My vet and I discussed his complications, and came up with a list of precautions for Shadow, which worked really well:
1- schedule the spay such that you can drop her off as close to her surgery as possible- less time nervously waiting and not eating or drinking.
2- ask to be able to pick her up as soon as she is ready and able to be discharged- she will be more comfortable in her familiar environment
3- arrange (if possible), for her to have fluids given during the procedure, that way if she does not drink, or takes a while to do so, she is well hydrated and less like to run into problems.
4- bring home a few 1ml syringes from the vet that you can use to syringe feed her some water if she needs it. I put a little bit of OJ into her water before using the syringe and she licked it all up!
5- the usual advice also includes pain meds before and after surgery, removing anything that will encourage jumping from her cage, and limiting her space to a maximum of 2ftx4ft for 5-7 days post operatively.
Most spats/neuters are routine with no complications. Odds are she will do great! Good luck and please let us know how she does!