I'm sorry, i have cats myself, hope your's recovers, i know that your sis feels bad about what happened, and maybe this will teach her a lesson, to be more careful (it could have been a small child sitting playing and she didn't see them either), or it might not have been her fault at all, the cat could have ran out in front of her, not to get in a debate about this but i believe that teenagers should not drive until they are 18. we give them a few weeks in school with a little booklet and BOOM there they are on the road, the same kids that arn't even responsible enough to feed the fish.
GOOD LUCK KEEP US INFORMED ABOUT HOW HE/SHE IS DOING!!!!!!!!!!!
Melissa V.