Fina had no other way out, everything she had come to care about had been taken away,"I'm not you, I can't walk away and pretend that this doesn't effect me." She moved to allow it to cut into her slightly, not bothering to even think about the effects or pain that might happen. While he held onto the hilt over her hand to control the movements, keeping her from successfully slicing her own throat open.
"They were all my friends and family. I cared for you up until this very moment. Just walk away, it's not so hard. It's what you do. I won't even make any noise." Fina wasn't strong physically, she couldn't hope to achieve what she wanted unless he let go.