I am going thru this with my mom

I have accepted she has terminal ALS. The Palledean Dr, psychologist, and social worker.. including the my parents priest; are all there to support my family.
It took me three days to understand "terminal" and what it meant. I am at piece with this about mom. I am doing everything I can to make quantity of life better for her. So is my dad, my daughter, my niece... not my sister.
Is this how people disassociate? Not accepting the fact? She lives a block away and does not come by at all. She did not come by during Mothers Day; however, expects things to be normal. Today, I have been here two weeks straight,... she stops by to show how she got her eye brows waxed. Stayed 5 mins. Total denial. Is it normal for me to be angry?
I really am trying to get her to connect with my mom again before she passes away, or is unable to communicate soon. Should I forget about my sister?
I would like anyone else going thru similar experiences about grief to share them here. That is before I pop again.
Huggles... it is tough.