Well, I'm not an expert, unless family hx makes you an expert. But, I'm glad you have her going to the doctor. Maybe the symptoms are from medicine that she's taking. If the diarrhea happens all the time, she may need a colonoscopy(diarrhea, feeling full and weight loss are some indicators or colo-rectal cancer). But, I am sure that it could be many things besides cancer. Try not to jump into the cancer scare everytime something is wrong(easier said then done), but always - always have her let her doctor know whats going on with her body.
Take care