I couldn't agree with Nancy more. Your Mom will be treated like royalty. Be sure to let your room steward know what special things he can do to help.
My wife's mother had Alzheimers and we would take her cruising long after most people would have. When we boarded, I would look up Elizabeth's room steward, immediately tip him $100 and then explain the situation. He would always spread the word on the ship to the other room stewards who were always looking out for Elizabeth. Ditto for the Maitre d' and waiter at dinner time.
Elizabeth had a rotweiller at home, so she would always ask the waiter for a doggie bag at the end of dinner. The waiter would always go to extreme lengths to make sure Elizabeth never felt awkward or embarrassed at any time. If I couldn't separate the doofie bag and Elizabeth after dinner, the room steward would. All in all, it was some of the best times our family had with her as she progressed and I wouldn't change a moment of it. You and your Mom will have lifetime memories from this cruise. I guarantee it.