You have the next 10 years to take care of her. Most assistance programs are income based. If her income is low, she should qualify for Medicaid. Perhaps she should apply now for public housing. There is a long waiting list, but seniors and disabled do have priority in some areas.
If she is not getting food stamps, you need to have her apply for those. Perhaps you and your siblings can chip in each month with $50 each or so to help her now, or you could put that into a retirement account for her when she does retire.
It is not too late for her to gain some new job skills. In my city for instance, the community college offers a 12 week program to become a Pharmacy Assistant. Check in your city for some of those programs.
Fibromyalgia is often triggered by emotional issues and once she gets something positive in her life, that might get better.
When she is 65, or whatever age is full retirement for her, she can collect on your Dad's social security account and she will get 1/2 the amount he gets when he collects.
Good luck, taking care of parents is something that many of us have had to face. But, keep in mind that she also has a responsibility to take steps to improve her life on her own, she is not helpless and you should encourage her to keep trying.