Oh my.
She is 15 right? She's most likely just fine. She has a car and a phone and has basic survival skills at this point! I don't really have any specific advice but my heart was pounding reading your post so I wanted to respond.
In general - deep breaths and let the adrenaline rush pass so that when you do talk with her you can be less afraid, angry parent and more calm, in control parent. Come up with a plan for what the consequences will be and a conversation that is concern and fact based rather then anger based. Give her time to talk too.
Feel for ya today. Parenting is a hard gig.