Oh I'm so sorry to hear this. I am a mother of 3 myself (my mother has the disease, not me) and I simply cannot imagine the emotional trauma she must be going through.
I think everyone approaches a terminal illness differently. My Dad had pancreatic cancer, diagnosed a few years ago. He fought it well and with great dignity, but at the same time he prepared himself and his friends and family for his death by organising his affairs, writing down some instructions for after he died and so on. My mother is different. She is in despair over her prognosis, and may remain that way to the end, whenever that may be. Neither way is "right" and I don't think it helps to tell someone to "snap out of it" or to be unselfish.
I know a woman who died from cancer a few months ago. She had 3 children aged 6-11. She and her husband agreed not to tell the children until the very end that she was going to die. They only learned about it the day before she died. They knew she was sick, but not how very sick. Her reasoning was that she didn't want them constantly asking her about "when will it happen." She wanted them to have parental security until the very end. I don't know if that's what I would do, and something felt wrong about it to me, but it was what she did after a lot of soul-searching and discussions with psychologists.
I guess what I'm saying is that your friend will need to find a way to deal with both the illness (the changes in her abilities) and she'll also need to find a way to deal with the fact that this illness has a poor prognosis. And as her friend you can support whatever approach she takes to that, even if you think it is "wrong" in some way.
As for dealing with the actual illness - fatigue is a big factor in this disease. Picking up her kids from school or taking them to birthday parties or sports on weekends so that she can take a nap is something that her friends can do for her. Also helping her to research some of the devices and facilities that are available so that she doesn't have to do the running around looking into software, devices and so on . . . if she's fatigued then her energy can be directed towards her family and towards making decisions based on research done by someone else, not in the legwork and phone calls.
You're obviously a good friend to be looking for ways to help. It's tragic for you to have a best friend who may not be around for the long term, and perhaps you need someone to talk to as well. We had a doctor tell us that any of us could die at any moment, and he's right of course, but it wasn't actually a helpful comment, keeping our heads in the sand about that is what keeps us all going! Stay fit and healthy for your friend so that you can support her as well as look after your own family. Hopefully she will have a supportive spouse too.
sesl