kitten behaving differently

Question
I have a kitten about 9 months old, a rescue from the local pound, her name is Ghost. Recently she has been behaving extremely out of the norm, for her, normally she loves to eat, hunt and play with the other kittens we have, they are all around the same age Ila and Crybaby are litter mates and are a month younger than Ghost, however Ghost has not had the desire to eat, play or hunt with very little desire to drink. I'm very concerned about this because it happened almost over night one day she was fine and the next very lethargic and not eating, she went an entire day without drinking. This behavior has gone on for approximately 3 days she has drank a little but it has to be brought to her she will not go out of her way to drink and just turns her head at the food.
My aunt told me that she may be going through her first heat, but in Oklahoma, it is standard procedure to spay and neuter all cats before adopting them out, and she was spayed, is it possible that she is going through a heat?

Answer
If she is spayed and this came on overnight, you need to get her into a vet asap. Kittens this young don't have a lot of body reserves for when they get sick and they can go downhill fast.

She could have too many things to list in here, and without knowing if she was tested for leukemia, FIV, FIP etc., I can't really say more other than she needs to see a vet.

When a cat goes into heat, they don't act like this at all. They are happy cats, rolling around on the floor, meowing at everything and everyone and rubbing on everything with their little butts in the air.

She is sick. Call your vet tomorrow.