How do I get my mother to eat in the dining room at the assisted living facility?

Unless she was verbally abusive before, then that is very likely coming from the dementia. If she's eating her food everyday, but chooses to do so alone then that's much better than not eating at all and such a choice is possibly one of the last things that she feels like she really has some control over. Does she get verbally abusive with others living at the assisted living place?

How about someone(caregiver) eat meals in room with her?
She is more comfortable in her room. Soon she will have good relationship with caregiver from ALH. This is my experianced when I was working with dementia pts