Would it be right to give people with dementia and sundowners a doll to nurse and help them be calm?

Thank you all you have been very helpful we will give it a go :)

This is done all the time. It doesn't have to be a doll, it can be a stuffed animal. My daughter had a cat that looked real.

My daughter crocheted a twiddle muff for my Mom and residents at her NH. You can see what I mean by putting tweedle muffs in search. There are also Twiddle blankets. They are more for people who tend to pick. Keeps their hands busy.

My LO functions at a relatively high level in her MC unit, but a few of her fellow care recipients do occasionally hold or walk with stuffed toys or dolls.
Although the approach didn’t help very much with another dear family member while she was sundowning, the atmosphere on the MC floor is VERY respectful, and not at all demeaning.
I’d try it.

When my mother had a short stay at a rehab and NH facility connected to her AL facility after surgery I saw a patient with a doll and it seemed to soothe her. I imagine it is not an uncommon practice. It certainly could be worth a try and thoughtful of you to try to find a solution to help her.

Mom's NH had a nursery of dolls plus a couple of very nice mechanical cats that could purr, meow and move their heads and several of the ladies liked them very much!

I wouldn't think this idea demeaning, necessarily. You're not saying "this lady is like a six year old," you're just exploring what activities might engage her attention in an enjoyable and positive way. Good thinking!

You could try bringing a doll with you, and at first playing with it yourself where your client can see what you're doing. If she shows any interest, encourage her. If not, no harm done. Hope it helps :)