Any suggestions to improve Mom's appetite or to get her to eat more?

I think about when I'm sick I don't really feel like eating. What have you tried to give her? Easier to eat food that is higher in nutritional value, like chicken soup, mashed potatoes made with chicken stock, or mashed sweet potatoes, mashed carrots cooked in broth, scrambled eggs, mashed avocado... She won't need a lot since her body isn't really using a lot of calories, unless she has a fever (then maybe also sips of Gatorade or something with electrolytes). When my son was really sick with Noro virus and couldn't keep anything down or in his doctor told me to give him 1 tablespoon of fluid every 15 minutes. Even if he can't keep it down some of it still gets absorbed. Staying hydrated will help your mom overall. Offer it, but don't force her to eat or drink.

Depending on her health speak to her primary doctor about an appetite stimulant.

I have used this before temporarily for my aunt and it helped a lot.

Has she been evaluated for hospice. If her organs were shutting down it will be painful for her to eat and the body to process food. DO NOT FORCE FEED HER!

How old is mom? Is she in hospice? I’m only asking because infection is often a normal progression of the disease in its later stages. They tend to sleep more, eat less, and struggle to fight off infections. If she rally’s and can fight it off somewhat (is she on antibiotics?) she may regain her appetite and begin eating again as she was before. Meanwhile, preparing her favorite foods and trying to coax her into eating them is worth a try.