The aunt is irrelevant. Tell AA they tried to sell the miles, didn't know it was against rules, ultimately used them for a family member, they never intended to break the rules and we're just trying to find a way to recoup the money they'd spent buying them which was a poor decision and cost them a lot of $$$ mea culpa, so sorry, etc. Ask them if they could at a minimum reinstate the aunt's ticket (assuming it was like 50k-150k miles) and volunteer to forfeit the rest. Worst case they say no, best case the full 300k is returned.