The only way to know for sure is to take Mom to the doctor for a complete physical. All of her meds need to be reviewed, blood work done, and your doctor will want to give her a mini mental status exam... MMSE. If he does suspect some type of dementia then you will probably want her referred to a geriatric neurologist or other specalist that is very familiar with dementia. ALZ is just one of the many types of dementia.
Yes, what you describe sounds very familiar to me. These were some of the first things we noticed about Mom. She would call and tell me a story, make a statement on a different topic, and then tell me the same story all over again. She appeared to be functioning ok alone, driving, and paying bills... until we search deeper under the cover that she kept up. In fact there were things growing in the fridge, sour milk being poured on morning cereal, she had almost stopped cooking, bills were being paid late, not paid at all, or being paid more than once. Pots were burned. The neighbors talked about Mom backing out into the street without stopping or looking. She ran over a piece of statuary and had not awareness that she had done this. Thank goodness it was just statuary and not a child. She could physically drive but frequently got lost, failed to obey traffic signals, not to mention the bumps and dings that 'mysteriously' appeared on the van. She was not taking medication as she should. She would either take too many or not enough. If she forgot a dose or two she would take them all when she remembered. Important papers were thrown in the trash and magazine ads were filed in the important papers. None of this was evident from a casual afternoon visit but a little digging turned up a horror show.
So get her checked out. If she suspects then she is probably right. Of course she is scared and worried. But perhaps it is something else as well which is reversable and treatable. It's better to be sure
I truly hope it's not one of the many forms of dementia but regardless you have found the right place. Welcome to the board and hope to hear from you again soon.
Love, deb
PS... be certain that somebody has her durable power of attorney, living will/medical directive/ medical poa, and names on all of her accounts. This will make it much easier to handle her financial and personal affairs once she is no longer capable. This needs to be done while she is relative aware of what is going on so don't wait too late.