In your town, there were killings going on. Killings that looked very witchy. And you were a witch, although it wasn't you and you didn't know any other witches nearby. Sam and Dean had figured that out from one look around your house. So, he separated you from your (adoptive) daughter and Dean was intimidating/interrogating you.

"You know, I have a hard time believing it's not you," Dean said, waving a gun around. "And I have a hard time believing that girl is even your daughter. She looks nothing like you."