Why do people who worked very hard throughout life, lived pure and holy lives fall victim to such a cruel death?

Yes I have wondered this seeing My own Mother of 87 years Who worked very hard throughout Her Life, and has been devoted to prayer and devotion to Our Blessed Lady. Mom is dying very slowly from Alzheimer's, a disease of the brain otherwise known as THE LONG GOOD BYE. Mom had seven Children, has twelve Grand Kids, and five great Grand Kids so far, Who are Mother's pride and joy. Mom always had only one wish and She expressed it to Us, IF EVER I LOOSE MY MIND ID PRAY FOR THE LORD TO TAKE ME, BECAISE I WOULD BE BETTER OFF GONE. A Mother Who was always giving unconditionally. Yet many times I have seen Person's Who Lived selfishly, and contributed very little but THEY PASS AWAY IN THEIR SLEEP.