You've done really well so far paying off your debts. To me, your sister's requests sound reasonable, but it's your situation. (not my business.) You sound very passionate. It would be great if you had a job that you love, that uses your talents. With all of your education, hopefully it would pay really well, too.

I'm a big believer in the concept of right work, right relationship. I think I would take a side job delivering pizzas or something for now to pay off the debt faster. Sometimes when you do that, new opportunities fall into your lap. It sounds like you don't want to have to pay back the loan, so you are in a job that is sucking your soul. I think you could find something you love and be able to get out of debt.