I'm coming a little late to this, but wanted to sway you with a different line of reasoning. 

Paying large chunks of medical debt is just about the worse thing you could do with that money. 

It's likely that your aunt is on disability or has insurance and is just needing help to pay the co-pays. If it's just for the co-pays then you could make a difference, but I wouldn't. Medical debt doesn't effect your credit and all hospitals have departments that handle repayment based on income. If she doesn't have any insurance the amount of money your grandpa gave you probably won't make a dent. 

Every hospital has plans for people like your aunt, 90  percent of the people you see at the hospital don't have the savings to pay for their services. She's just going to have to do the same as every other American and eat the medical debt.