Are adult foster homes a good placement for dementia patients?

There are very nice ones and some not so nice, like anything else. I wish I had been able to find one for my DH aunt. I was too far gone and so was she when I had to place her and hadn’t found the right one. Others here on AC have used them and liked them.
Mom is not going to volunteer. You need to tell her whatever it takes to get her there. Perhaps the house needs painting, fumigating, etc. True story, my aunts house flooded and that is why she went into care when she did.

My BIL is in such a facility, but it's not called a foster home. It is an adult dementia-care facility, board-and-care type. The owners are former RN/caregivers. It's a nice home in a good neighborhood where families live, and you wouldn't know it was a facility of any type by riding by. It has a swimming pool and 24/7 care by the same caregivers who took care of BIL's mother in her home. There might be 8 residents. He has his own room but shares a bath with one other male resident. He has been happy there for many years. In Florida.

You are referring to a home care that is a house correct? I found that my daddy liked it better than a big facility. He got better care, he got personal care and he was never left alone. I treated the caregivers as family, I would take them dinner, or treats, I learned their birthdays and brought them a gift. I would talk to them about their family and give them some of my time and learn of theirs. This kept communication open and friendly. When he was in a major facility with over 100 people they didn't have time for him they left him and did not care for him as I would have expected. Tell mom it more like living at home instead of living in a home.