The situation does highlight the difficult relationship between mothers and their daughters, a stormy course for most of us at one point during our upbringing. Daughter's act out and mother's act out in estrogen-fueled ways. Thankfully, most daughters regain their senses during the late teenage years. Most mothers become cool again around the same time.
There are millions of young women who have also turned their personal tragedies into incredible displays of triumph. When one is able to do that, they are entitled to forgive, forget, honor or disavow anyone, anytime they need to. At some point, you get tired of hoping that your family member 'gets it' and you have to keep your own life moving.
Mother and daughters are bound together by blood but not always choice. The ease of the relationship is often softened like well-worn leather by use, wearing, and sweat. It requires a willingness to work and also love and forgiveness. Not easy, just like the decision to pay off debt belonging to someone else. Hey, in some ways writing a check may be easier.