Would your sister go over and get it and then bring it to you, with the understanding that she could borrow it any time she needs to. If you've gotten close during her divorce, she'd probably be glad to help out. My mom passed away and my dad has remarried. Some of the things he does now, I don't even believe. But he's 85 and probably not playing with a full deck. When I go back to Lubbock for short trips to take care of business there, I always try to visit him. He lives another 3 hours away. So, 6hrs round trip because I won't spend the night. Half the time, he tells me not to come. I think my stepmom doesn't like for me to see her house dirty, because she knows what a neat freak my mom was. (She raises dogs and doesn't do a good job of picking up after them. They live in the country, and there's always mouse droppings and bugs.) I just say ok and I'll try to catch them next time. I try to be philosophical and not take it personally, but it's not easy.
Edited to add: Just saw your post that he said you could use it. I'm so glad. He just needed a little time to wrap his head around it.