My perspective, coming from a dysfunctional family, including siblings with addiction issues, etc... I think your mom's financial situation is only a symptom of a larger emotional/psychological problem.
My opinion is that no amount of financial help will do any long term good, rather I would focus on encouraging her/be supportive of her getting help. Some help can be free (a previous poster had suggested al alon), others like counseling may have a small cost. If you feel the need to help her financially in the near term, this is what I would offer to pay.
As far as the money your mom has paid you, this is a personal moral judgement on your part. You are the only one that can decide if it's something you should somehow pay back in the future. Personally, I can certainly see how you feel were wronged. The unannounced BK (given you could have rectified the loan situation with warning), coupled with poor parental advice on school, would probably have me resentful and feeling owed as well. If you decide that you should "repay" her, I like the advice another poster gave. Save 24K (less any counseling/mental health support fees you help with in the interim) and invest it so that you have money to help your mom in the future. The path she is on; poor health, stress, lack of finances, means that unless she chooses to change, in the next few years she will likely be unable to work. Then you will have a mom on disability, with expensive medical bills and no other means to support herself. You can repay her then when she will need the money to maintain a forced, but very basic lifestyle.
Lastly, if you haven't already, make sure you take care of your own mental health. I don't know you personally, but coming from a family making dysfunctional choices like this rarely leaves one unscathed. Invest the time, energy and money (if need be) in yourself to make sure your future life and relationships are healthy. This investment will produce returns far exceeding any index fund.
Good luck my fellow life traveler!