Sorry to hear you are having a situation
I hope all runs smoothly a the vet with the Xray.
Most spayings run smoothly. I was surprised to hear you are having problems.
I think my Vet told me not to feed my dog the first day. I don't recall any advice about water etc. My dog did have a pain shot before she came home and was very still for a couple of days.
Each dog is so different and circumstances are different.
One cannot rule out problems but they certainly are the exception to the rule for routine procedures like spaying.
I hope the xray shows nothing and that all you need to do is to keep her quiet. Dogs can go a few days without eating huge meals. But they do need food and water eventually.
Keep us posted with her updates as we are all worried, just not as much as you are, that's for sure. We all worry for our beloved furry pets.
Good luck at the vet's.