I am sorry to read that Beth. As you say we only have one mother and I know it never seems long enough to you, but 79 was a good age generally speaking.
We are sad at the death of a loved one of course, but why are we sad? It is because we will miss that person and the things we would say and do together. Their life has ended, no more pain and suffering for them if they were that way but we have the pain now. I know it won't seem that way for a while and you now have a "Year of firsts" to endure, but in time, the pain decreases and happiness begins to fill the space. When we remember them, it's the happy times that we recall, not the sad.
I believe a person is only really and truly gone when no one remembers their name or speaks it and they have become forgotten by later family members.
Take care of yourself and remember that you were loved and always will be, it's just in a different way now.
Peace and love to you Beth and my sympathies.
Love,
Clare