My mother has dementia. She believes everybody is talking about her. She’s on 200 mg Sertraline. Any advice for medication?

Your mom is paranoid which is very common with folks with dementia, and there are medications that can help with that. Like already said, you should talk to her doctor about what perhaps can be done to help her with her paranoia.

Medications always are best discussed with the medical doctor who is familiar with any particular individual patient. But I surely do wish you the very best of luck. I know that you also know that it is completely the "norm" in dementia to have this sort of paranoid ideation; it's a hard one to beat down.