You can soak some of her normal pellets in water and feed the slurry to her by syringe. That works almost as well as Critical Care. You’re right about treats, in this situation you don’t have to worry too much about sugar content, she can get what she wants to eat. The important thing is that she eats. It’s common for bunnies to not want their pellets after their spay/neuter. I don’t know why, but they tend to prefer veggies, especially fragrant herbs (parsley, dill, cilantro, mint) and fruit and also hay for a couple of days.
Make sure she doesn’t get cold. A bunny that’s not eating much and has been under full anesthesia can get cold “from the inside”. That’s very dangerous, because it can lead to the body shutting down. If she’s very inactive and her ears are ice cold, try warming her up with a warm water bottle or hand warmers wrapped in a towel. Make sure she has space enough to move away from the heat if she doesn’t want it.