Is there a law in NY that enables Elder Services to be able to step in and place a parent with dementia in a nursing home?

Not much detail here. I can’t imagine though, how any law on the books could force someone who is still in control of their facilities out of their home and into long term care. You could consult an attorney to see what you would need to do and follow the letter of the law.

Perhaps you could speak with the person’s physician and enlist their help. They usually have staff on board who can assist.