Congrats LK!
I know how you feel, I still refuse to borrow money from anyone to help me with well anything, except if I'm broke and someone offers me a cup or tea or coffee I will gladly take that
But look at this way, like you said, most of them used it to buy drugs and those grand kids are in prison now, I am sure she was more than happy to give you money for your education and is proud of you for it. It's probably reassuring to her to know it's going to something to better yourself.
Like Rmdctc said pay back with interest when the time comes. Or try to think of it as another loan!
I know how you feel, but things will be okay, and your getting the last of your education in!! yay!
Blessings
Sparrow