I am not a medical doctor, of course but I strongly urge you to share your concern with your aunt's doctor and arrange for her to be tested. Although Alzheimer's disease cannot be cured at present, I understand its development often can be slowed with proper medication.
But regardless of the exact diagnosis, your aunt's forgetfulness is certainly a matter of concern. After all, she could easily forget and leave a pan on the stove, or forget which is the brake pedal in her car, or in some other way bring harm either to herself or to others. Now is the time to try to help her, not after some crisis arises that could have been prevented.
The Bible says, "Pity the man (or woman) who falls and has no one to help him up!" (Ecclesiastes 4:10). You and her other relatives have a responsibility to monitor your aunt's condition and, if necessary, to take steps to help her during this difficult time in her life. Wouldn't you want someone to do the same for you if you were in her position? Jesus' words apply here just as much as they do in other situations: "In everything, do to others what you would have them do to you" (Matthew 7:12).
Elsewhere you mention that your aunt has always had a strong faith in Christ and no matter how forgetful she becomes, He will never forget her. May that comfort you and may it also challenge you to grow strong in your own faith while you can.