i think you are letting yourself think about this too much... she will be fine... if you are confident in your vet.. things will be fine... if your vet is the problem then you might not want to go through with it with HIM/HER. if spaying is something you want to have done.. then go tomorrow and things will be ok... we ALL doubted weather or not we should do various things... i was sick the night before i had to bring layla in to get baby teeth removed... should i put her under again.. and so soon after her spay.. i was a mess.. but she came out just fine... the sooner you do it the sooner it is behind you and you never have to do it again
it will be ok
we are here for you tomorrow... i'll be thinking of you both!