Alzheimer's is a devastating disease that takes a terrible toll not only on the person who has it, but also on all those who are close to them. Not only does Alzheimer's result in severe memory loss, but at times it can even lead to serious personality changes. I've seen this happen to some of my friends.
God knows what your aunt is going through, and He knows she's no longer responsible for her actions. I don't know why this kind of personality change occurs, but sometimes it does, and to the best of our present knowledge there's nothing your aunt could have done to prevent it. It's almost as if the personality that God gave her has now been stripped away. The prophet Hosea compared the people of his day to an old man whose ability to think clearly has gone: "His hair is sprinkled with gray, but he does not notice" (Hosea 7:9).
Whatever the reason for the changes in your aunt, God doesn't hold her accountable for her present actions, any more than He would hold a small child responsible for acting like a child. God loves her, and His love will never leave her. The Bible promises, "Even to your old age and gray hairs I am he, I am he who will sustain you" (Isaiah 46:4).
Never forget: We are saved only by God's grace, not by our own goodness. It's true for your aunt -- and it's true for you. Is your faith in Jesus Christ, no matter what happens in your future?