How can I plan for supporting my mother until she's 65?

I am looking for a little guidance on what to do to start planning for the care of my mother. My mother is only 53 right now, but I am already financially supporting her by paying her rent and utilities. She is attempting to find a job, but has had little luck since she has little education, no drivers license, and a bum knee that causes her to walk with a limp. To put it bluntly, she is 53 going on 73 due to years of alcohol and general abuse to herself. She no longer drinks, but that does not reverse the bad shape she is in for her age. She is too young to qualify for medicaid or SS and it would appear to me that even if she manages to get a job soon, it will only be a delay to what is going to ultimatly happen, which is my sisters and I eventually supporting her. She has NO SAVINGS at all, and at this point no medical insurance, nothing. I need to start coming up with an action plan on how to start planning for her care as she ages. This could be a 20-25 year haul here. I make okay money, but I have a family of my own, and I DO NOT want to put my children into this very position, because I exhaust all my own resources caring for my mom. I really need to start making a plan on how to take care of my mother for the long haul without becoming a pauper myself. Moving her in with me is an absolute last resort....she has a very low tolerance for children, even her own grand kids, and frankly, she is a bear of a personality to live with and subject my husband and kids to on a permanent basis, so we must avoid that until it is the absolute last resort. That being said, I have to plan out how to take care of her if: she is not able to find employment she can do, or she becomes very ill, or if she simply ages to a point of not being able to be on her own any further. Where can I start to try and head this all off at the pass? All information of how to plan or what to think about or investigate is very welcome.