Bringing in a poop sample is probably a good idea. Some medications you should ask about are Albon and Metronidazole.
What brand of food are you feeding? At this point it's a good chance that the stress of the spay and the medications just really messed up her stomach, but if you are feeding store brand foods they are not going to help. That would be like if you were really sick with a stomach flu then decided to continuously eat fast food, you'd probably feel really yucky too.
Depending on what you are feeding, you may need to try a different food that will be easier on the stomach. There are some holistic pro-biotics that might be able to help, as well as adding some pumpkin to the diet. But if your kitty has something like giardia or coccidia then it's possible the surgery threw that into full effect and that's what is making her sick.