There are a lot of free (county/state) rehabs out there. Also, many low cost ones. I went to rehab without having any insurance in TX. I thought about going again a few months ago and found several here in GA. (my counselor gave me 40 pages to research and 80% were free or sliding scale).
What state is she in? I would be happy to do some research for you if she is willing to go into a facility. It has to be her choice, no one can force someone to get clean. However, if son kicks her out, she may have no choice but to go to rehab for roof over her head.
So sad for the son. He has to think of himself, it's hard. He will have to kick her out if she won't follow his rules. All involved are in my prayers.