Well, that was an ominous beginning to a statement-- and Sam was more than capable of filling in the rest. He'd seen the creative ways that witches could kill people with magic. But if there was one thing he was no longer afraid of, at all, it was his own death. He wasn't afraid of pain, either; he doubted there was much she could do to him that was more painful and miserable than being tortured in hell, or being purified by the trials.
And she needed his help. She was a witch who wanted to control her powers, use them for good. How many times had he tried to help people, convince them to do the right thing? She didn't need to be condemned and hunted, at least not now. Maybe one day her powers would take her down a bad path, as had happened so many times. But he might be able to prevent that.
He knew one other thing, too. If she was trying to control her powers, frustration wasn't going to help. It might well do the opposite.
"Hey," he said gently, taking a step closer. He hesitated only for a moment before reaching out and putting a light hand on her shoulder. He was prepared for the possibility of an electric shock, but the risk seemed worth it. "Take a deep breath, okay? I know a little bit about controlling powers, I can help you. I will help you, if you'll let me."