If she has diarrhea she may have johne's. Hardware or a blockage are also good guesses. Also check her mouth for a growth. Lumpy jaw or woody tongue causes drooling and won't let them eat but with woody tongue, her tongue would be sticking out of her mouth.
I had one like that years ago that had a big cancerous growth in her mouth that blocked her throat. It was not noticeable except when you looked in her mouth. Either way. I would ship her at the first opportunity. She will be a downer sooner or later. I would bet she is not putting out much milk anyway.