I've just posted this on another thread, it might help you. But it was not designed with a diabetic in mind, so you might have to ignore some suggestions. I am sorry, I have no experience of diabetic diets.
I would try tempting your mum with anything she might fancy, and do not worry about its normal health properties. I am reasonably fit, but when I am stressed my appetite disappears. I eat small meals frequently (I often can't eat a full dinner), cheese on toast, an omelette with ham and onions, soup (I love soups - vegetables will help with the bowels, lentil soup is full of protein as well) with bread dunked in and a sprinkling of cheese on top, yogurts, trifle, banana and custard, banana and ice cream, fruit juices will also help with the bowels. Things like bran are probably too heavy, try porridge with a spoon of jam, brown bread toast and honey, scrambled eggs (maybe with tomatoes and cheese), fresh fruit salad and yoghurt or cream even (don't worry now about cholesterol). Anything your mum fancies, basically, that will keep her going. Even a bar of chocolate has some protein and of course calories. Cups of milky coffee. Protein and calories. Dried fruits for Vitamin C as well as fibre, apricots, sultanas, peaches. Nibbled throughout the day. Avoid nuts, great for young people but could cause choking in the elderly.
"Empty" calories in a glass of sherry or port. Not allowed to suggest that nowadays! But they ARE calories and if your mum enjoys a drink, why not?
But you can also get powders to mix with foods to add calories and vitamins/minerals, I have forgotten what they are called, but you can stir a spoonful into a cup of coffee, or a tablespoon into a bowl of soup.
I do hope this helps, I went through it very thoroughly when my dad was ill. Forget the normal dinner of meat and two veg, but I don't think you have to resort entirely to baby food. Though it is probably a lot of effort on your part. But you can buy vegetable soup in cans, never mind the extra salt they might contain, it won't do your mum any harm for a short while I would think.
Let us know how you go on. I am sure others on this site will have much better ideas than I have.
Love
Margaret