I'm so sorry about your mom. That is a tough thing to hear, and takes quite a while for everything to sink in, I know.
My sister was diagnosed with stage 4 liver cancer in August 2006. The Drs thought she only had about 6 months of quality life left. She held out for 26 months, and was active right up until the last 2 months.
We learned that my sister did not want to spend time talking about or thinking about her cancer. She had 6 children between the ages of 3 and 16 when she was diagnosed, and the thought of leaving them was very hard on her. So we did everything we could to keep everything "normal" for her. We talked, laughed, cut up, and argued as we had before she ever got sick. It helped her for life to continue as if nothing was wrong.
We did get her some of her favorite books for reading when she was getting her chemo treatments, and a portable DVD player. Sometimes it would take 6 hours or more for the IV drugs to run, and that helped her pass the time.
We also went about the business of creating memories for her children. (You could do this for the grandchildren if there are any.) We sent her family to WDW for a week, as it was always on their "to do when we have time" list. We rented a beach house for a week, and went with the whole family. Little things to give the kids extra, happy memories to combat the sadder ones sure to come. We also made sure to get family portraits made while she was feeling good, and before she lost her hair. We went back and did it again 18 months later.
I hope you are able to find some of this info useful.
