Complan may be the way forward as a temporary supplement but not a substitute for food. There are probably similar products that do the same thing, it might be worth investigating.
Ready meals would depend on her personal preferences. For instance, does she prefer, English, Italian, Indian, Chinese. Most supermarkets carry a good range.
Maybe start with child portions and include light desserts like individual yogurts, mousses or jelly.
She may be partial to a bit of toast or cereal - not necessarily just at breakfast time. Most bread and cereals are vitamin enriched and many contain a lot of calories.
I hope, at least some of this is helpful and I wish you, your sister and your mother all the best.
Light hearted - Confessions of a Teenager?
Best Supermarket Substitutions?
Only 50% of middle age adult manage more than 1 brisk 10 min walk a month.
