Hello! Please remember that my response is for information only, we are not establishing a therapeutic relationship.
It is difficult to lose someone we love no matter what the circumstances, like even if they are elderly --even at 95, 98, or 100!
Anger is part of the grieving process, it sounds like perhaps you are anticipating the grief already, even though you have not lost her yet.
Does your mother ever talk about her own death?
That makes it difficult to know how she feels about death. If you knew that she is at peace with it, perhaps you would be as well.
But --regardless, one important factor here is that it hasn't happened yet. And, anxiety is all about anticipation --of things that have not happened.
If you can find a way to say, "I'll deal with it when it happens," and stay in the "here and now," the anxiety would subside --but that is difficult to do!
It looks like my last comments were erased.
I basically said that she sounds likea really neat lady --and is probably at peace with where she is in life.
I said something to the effect that it's OK to get angry (part of the grieving process), but you don't want to jump the gun with anticipating her death (which is what anxiety is all about --anticipating something that hasn't happened yet).
It's hard, but staying in the "here and now," and saying "I'll deal with that when it happens," is an important key to controlling anxiety.
And --you want your focus to be on enjoying every minute you have with her.
Are you a person of faith as well?