She brings it up in a certain group and blames it on her Dementia. She is not angry, just not thoughtful. Haven't seen or heard her do it again. Is this part of Dementia?
Probably. Social filters are controlled by a specific section of the brain, and when they are affected by dementia they can stop working so well. If a normally kind and tactful person suddenly blurts out rude, hurtful, personal comments in public you would certainly be suspicious - especially if they don't seem even to be aware that there's a problem.
You may find this happens more as time goes on.