How can my husband have his mother placed in a nursing home?

When you try to reason with someone with dementia they will indeed become combative because their disease takes away their reasoning skills. It won't work. Instead, it is frequently advised to just go along with it if it doesn't harm anyone and it does not seem her carrying around a doll is any harm to anyone. I assume her lack of being able to follow her son's line of reasoning is not the reason you are looking to place her.

How can he place her in a facility? Start doing research on the ones closest to you. Do tours of the ones that would be the best fit for her. Speak with her medical professional and find out what level of care she needs so you don’t need to move her again in few months when she gets worse. She may need to be evaluated. While you’re there, have her tested for a urinary tract infection. That can cause the behaviors you’re seeing.

If she cannot self-pay, file for Medicaid.

And, your husband needs to understand that you cannot reason with someone who has dementia. The doll is a real baby to her. This is a common delusion for women. He should never, ever try to take it from her or hide it from her. He may need to speak with her doctor and find out about how people with dementia act.

I volunteer (reading aloud) in a local nursing home, and we have a resident who also carries around her ‘baby’ doll. Everyone plays along, it is a comfort to her and quite harmless. Perhaps forget about the doll, and just worry about the combativeness. It would be a pity to fall out just because she is annoying you by being ‘silly’. One bright side is that baby isn't incontinent!