"You think I put myself in danger just because of something you said?" Okay, so she totally did. And it probably was completely partly his fault. But she was grateful for him being there now, and grateful for him covering up her bruise and she just couldn't sit there and let him blame himself. Even if it wasn't tearing him up inside, it was still bothering him or he wouldn't have cared.
"Trust me, you are not that far under my skin. I did it to prove it to myself. And maybe to piss my parents off or something. I don't know." Her lie detection was going off on herself, but she ignored it. "But it had nothing to do with you, okay? So you can stop blaming yourself or whatever."