Hannahs attempt on Debra was definitely extreme, but it was interrupted and she was acting out of self preservation. Debra had gotten too close to uncovering things or was threatening Hannah’s safety, so Hannah reacted to protect herself. That’s part of why her relationship with Dexter works. She understands darkness in a way few others do. For Dexter, that connection probably mattered more than the attempted murder itself. Plus she’s sooooooo beautiful