I agree it could be a health issue.
I also agree that if she likes the cat food, at this point I might just let her eat it, at least some of the time, if the vet says it's not a problem.
You can do the boiled chicken, hamburger, rice thing if you want, but once you start doing it, it may wind up being the only thing she'll eat unless you wean her off, and if this a "preference" issue over an "illness" issue, it may be hard to get her to go back. (Definitely not something I'd do in a younger, healthy dog with the exception of short term due to illness.) Unless you don't mind making it for her every day, then it's probably not an issue.
I hope it's nothing serious. She must be a beautiful dog.