I'm not a doctor but it sounds like some typical changes associated with age. The heart gets a bit weaker, there's bound to be some calcification here and there and because of osteoporosis, we shrink in height. It seems older folks just don't enjoy food as much or have as much appetite either. My parents are close to the same age as your Mom and they've started drinking a supplement (like Ensure). It helps with calorie intake and is not as bulky as a full meal. That's my two cents worth.
Well, the time comes in all of our lifes when we need more personal care, support in our every day life. It is it for your mother. Love her ,comfort her, it seems the independent time must be replaced at least partly. Try to give her the best food ,best care ,you, family...
Have lots of quality time with her, best I can think of.
Loneliness can kill. Happines in all age can save us from dieing for very long.
My best to her and you.