Poor woman, I think I'd be in tears as well.
I would be too, but they'd be tears of frustration and anger.
I am curious though as to how he got her keys (and her car) in the first place if he was her brother. And I would also like to know in what universe his brain lives in where it is his sister's responsibility to either drive him around or provide him with her car? 
After the Christmas travel debacle involving my irresponsible snowflake brother, I've resolved to change the way I interact with him. Because I don't want to end up in the kind of position above. So where as I would normally just go with the flow or just stew silently about his self-centered antics, I am calling him on it and frequently. For instance, earlier this month, brother came into town on a quick overnight trip and asked if he could stay at my home. I told him that was fine, but he would have to sleep in the second twin bed in my son's room since we don't have a guest room. DS is 4. Bro said that was fine.
During the course of his 24 hour visit, he griped almost non-stop:
- about having to sleep in a "crappy twin bed."
- about my kids being too loud. They weren't, they were operating at normal conversational levels. But they were talking during a sports program he wanted to watch and he expected complete silence.
- about not being able to take a four hour nap in my son's room during the day because my son kept coming in to get toys or books to play with in the living room. Sorry, it's my son's room and if he wants a toy, he can get it.
- about my kids getting up too early in the morning (to get dressed for their school day) and waking him up before he was ready.
So when he left, I pulled him aside and quietly informed him that hotels have nicer beds, TVs he can control and kid-free rooms. So the next time he comes into town, he should book a room in one, because he is not going to spend his time in my home criticizing my hospitality and making my kids feel uncomfortable in their own homes. I'm done.