Oh my goodness, yes, I would definitely change vets. Are the two you have seen both at the same practice? Tigerlilly has great advice, ring a vet school if there’s one near you and ask for help, otherwise ring round friends and family until you find a vet they can recommend. If all else fails, look in the phone book under veterinary services.
Has she not been admitted to their clinic and put on a drip for fluids and feeding? Have they done blood tests? Has she been tested for all the usual kitten viruses and serious illnesses? It seems appalling to me that they can have charged you that amount of money but not admitted her and not given you a clear idea of what is going on. Is there good communication with them (it doesn’t sound like it)? You need a vet you can trust and work with, and who will explain to you exactly what they’re doing, what they’re thinking and what they’ve eliminated as a diagnosis so far.
Your poor little kitten. The most important thing is that she doesn’t get dehydrated, which is why I would have thought they should have admitted her. Is she drinking lots of water? Try to keep her fluid intake up. Pedialyte is the best thing to give her, and you can mix a little of it into her food as well. You don’t say if she’s eating. If not, there is a high-energy paste (nutrical) you can give her a little of if her energy is failing — also a little corn syrup smeared on her mouth (nothing she could choke on) is good for energy. Other people who are more knowledgeable will come on and give you better advice so please keep checking back.
But yes, find another vet. And get them to show you how to inject fluids into your baby, to keep her fluids up. Four thousand dollars and no blood work seems to me unconscionable!