well you don't need a professional for this really
62 year old female with severe muscle wasting, first step is getting out the house and walking, down the shops etc. Can she climb stairs? This is a good next step. Basically just eat a high protein natural diet, it's not complicated. Lots of lean meats and potatoes. Sugars will just get her fat, not really the best move but if the weight gain is hard then ice cream is always good if she is like every other white middle class female I know
Gradually progress to more difficult exercise. Swimming would be good, very low impact but if there is arthritis this could present a problem unless you can find a warm pool. Hope the recovery isn't drawn out too long