Don't know your age but I would put some level of focus on getting away from there as soon as it becomes possible so it's not in your face constantly pointing out the problem by living around it.

You not only can't change her but you also can't change what is in her future. We all make choices in our lives & have live with the consequences those choices cause. If they are unwilling to address the problem we just have to realize it's out of our hands & walk away....that doesn't mean you can't or shouldn't be there if anything changes....but for the time being its best to detach from the situation....(called self-care)