Rheumatoid arthritis, and possibly soon to be single parent...
It is hard to watch a friend in a bad place, and not be able to help.
She will have to reach the point that she really wants to improve the situation before she can hear your suggestions. Maybe you can research available resources in your area, (women's shelters, arthritis support groups, parenting classes, I don't know what else might be available and appropriate in your area) and have them ready when she asks.
Until then, she needs non-judgmental support, and a good friend like you.
You could read "When the body says No" by Gabor Maté MD. He's totally non-judgemental, no blame, but has brilliant insight. Reading it you'd get a very good look at how your friend arrived where she is, which gives clues as to what needs to happen in order to move forwards. It's an incredible book. Perhaps after you read it you could read it with her. With insight, perhaps she can dip inside and find the resources within herself to make a break for the sake of her child.