I am sorry to hear you are worried about Mocha, and I am worried, too. My name is Rebecca. I am a veterinarian and will do my best to help.
Any time a dog develeops a picky appetite like this,and only wants special food or table food, it cam be a sign that they do not feel good. The weight loss really concerns me.
There are many possibilities: an infection, pancreatitis, liver or kidney disease, pain (joints, back, neck, internal), parasites (is she on heartworm preventative?), even cancer. When I see a dog that is not eating well, I start with a thorough physical exam: palpate internal organs and lymph nodes, take the temp, listen with a stethoscope, check for dehydration, check to see if the gums are normal bright pink or pale, feel the pulses, palpate legs and joints and back for areas of muscle tension. That may start to tell me where the problem is, but sometimes I need to do blood tests as well, or Xrays.
If you look at her gums, are they pink? Any vomiting?