Hi lymara, and welcome to Talking Point.
I'm so sorry to hear about your worries over your mum's weight. I don't have any personal experience of big weight loss, but we do often struggle to get my mam, who has Alzheimer's, to eat properly.
At these times, we (my dad and I) have found that it's more important to get calories into her rather than worry too much about what she's eating. She prefers sweet things, for instance, so whereas she might not eat a main course she will often relish a pudding, sponge and custard for example, and although she refuses to eat most vegetables she does love fruit, so a bowl of fruit salad and ice cream usually goes down a treat.
Also, little and often could be better than expecting her to eat a big meal. We try not to over face her; better that she eats a small plate of food than pushes a large portion away without eating anyhing, simply because it looks too much for her to manage.
Finger foods, things she can carry around with her sometimes also work, rather than sitting at the table.
Plenty of cups of tea, with cake and biscuits, again simply for calories are another option.
Does your mum have a social worker? If not, it may be time to contact social services and get them involved. Alternatively talk to her GP. I believe that there are fortified drinks that can be prescribed although I have no experience of these, but I know of other TPers who do.
I'm sorry, I don't have any suggestions regarding your mum sleeping a lot, but I'm sure others will be along soon to help.
Do keep posting, you are among friends here and it's a good source of advice, support and comfort.