She does need to eat, if she won’t eat you’ll have to soak pellets in water and feed the mush to her with a feeding-syringe. If she eats when you hand-feed her hay or greens or anything at all, really, then keep that up. Poop will be weird for some time, that’s normal after a spay.

As Vienna says, you need to keep her warm. Both the surgery and the pain meds lower the body temp in a rabbit, and that’s dangerous. Not eating also prevents the body from keeping itself warm. If you give her a heat-source, (hot water bottle, hand warmers), make sure she has space enough to move away from it if it gets too hot for her liking.

It’s great that she’s drinking and peeing. All poop is good, even if it’s squishy and malformed.

If you can’t get food in her very soon, you need to take her back in.