Rodney's death. Especially since he could have done so much to help Justina deal with being turned into a vampire.
Leila's origin story was being struck by a bolt of lightning, imbuing her with the power to wield electricity. Her mother, attempting to help her, touched her and was electrocuted. It turns out her mother didn't do this out of mindless panic. She possessed legacy magic, which can be transferred from person to person and takes the form the recipient most needs at that moment. In Leila's case, it made the otherwise lethal electricity a functioning part of her. This means her mother made a conscious choice; her life for her daughter's.
