YTA. I'm not going to say esh because I have dealt with entitled people in the past who think they're entitled to free rides and use my stuff. You can deal with it in different ways.

You have no idea how bad a criminal record fucks over the rest of your life, and I don't think anyone else does either. Everyone is saying theft is theft, but that's not even the case here. You LET your sister use your car. You were not firm about taking the keys away. You were just butthurt because someone was taking advantage of your generosity.

Your sister might even lose her job over this. Your sister may never be able to get a really high paying job because of this. And before anyone tells me that it's theft and laws have consequences, I really want you dig down into your own past and think about how many times you've gotten away with something that you shouldn't have.