I went through something similar with Taz a few months ago. He wasn't eating as much as normal or drinking. I took him to the vet and he was very dehydrated. Do you know how to test for dehydration? Pull up the skin on her back and if it takes a while to go down she is dehydrated.
Anyway, Taz went through many tests that luckily came back fine. But it still didn't answer why he was throwing up all the time. So we changed his food. He was on Purina Vet Diets o/m (which can only be purchased at the vet) and then tried a couple others. I really didn't like the fact we were changing his food so much. Finally we put him on the Purina Vet z/d, which is for sensitive stomachs and he seems to be back to normal. He has not put back on the few pounds he lost while he was sick, but that's okay, he has a few pounds to spare.
Not sure how old C.P. is but Taz is over 10 years. And since all animals are different, you can't use my example in relation to your C.P. I would have never figured it out if I hadn't taken him to the vet.
Anyway, #1 thing to do is take her to the vet.