Cat ripping hair out

I have the same problem with my Bengal cat. She rips her hair out and we have no idea why. We're in the process of changing her food. My Vet put her on Prednisone and Amitriptyline but nothing is working. We are retired and play with her a lot. I'm really upset and wish someone could come up with an answer. I talked with the Breeder and she says this is a first. If anyone can help I'd so appreciate it.

Welcome to The Cat Site, sorry it was under these conditions.  

What are you feeding her and what are you transitioning her to?

Is this sudden or has she been prone to do this?  Any thing different in her life--new people, new house, new cleaning agents?

How long has she been on Amitriptyline?  It can take several weeks to begin working.

And, not all antidepressants are equal, sometimes it takes a combination of two.