I'm so sorry that you and your family are having to go through that, but I really believe that it's probably harder on you than it is your mother.
When I first found out that my healthy, handsome husband had cancer, I had to get rx's for a sleeping pill and an anti-nausea pill so that I could eat. I'm down from 138 to 123...I don't recommend the grief/panic diet. Things are looking up for us, but this is going to be a marathon, not a sprint. Maybe that's what helped me the most...the realization that we're going to have to be on top of this situation for years and it won't help anyone if I end up with a coronary. Please take care of yourself. Best of luck to you.