What should I believe here?

I have been having some problems with my friend. I know she has a habit of dating less then reputable people but now she's gone to dating people over in other cities. Her latest is some 18 year old from across the county and she's only 15. And, to make it worse, she told me she slept with him on only the second time she's physically met him. And now she's pregnant. But after I told her it was a gross thing to do and kinda slutty, she said she was just joking and not pregnant at all. She never said she was joking about the sleeping with part. Do you guys think she was just joking or is there more to this then what she's saying. I got kinda creeped out from it and I haven't talked to her in a couple days or so. I've known her for four years and she's dated some really creepy people those years, but never said she slept with any of them. And on top of that she talked to me about running away to Las Vegas with me so she could work as a prostitute and we could live there! You guys have any idea what is going on here, should I be worried, and what should I do here?