I would also not blame the cat food too much. Our little one liked cat food too when she first came to us, and when she got very ill, the vet wanted to blame the cat food. They all said it was too high in protein. However, my husband checked the bag, and the puppy food was higher! Do you have any plants in the house? Also ours is nearly 7, and she occasionally gets ill for seemingly no reason.
We are always at a loss. Anyway, good advice from everyone, keep her hydrated. Keep a very close eye on her, and if she begins to act weak, get her in ASAP.