|Episode(s)|| 8.04 Bitten|
10.04 Paper Moon
She began a relationship with Michael Wheeler. After Michael starts becoming a werewolf, she was there for him throughout the ordeal. She was turned by Michael's roommate, Brian Wilcox, into a werewolf and in anger rips into Brian thus killing him. She leaves a video behind for Sam and Dean to watch and promises to them that she won't feed on humans but only animals.
She met Michael Wheeler, while he and Brian Wilcox were filming in a cafe, and soon started dating. Throughout Michael's ordeal of becoming a werewolf, she supported and tried to help him, however she began to develop a dislike for his roommate Brian, who also began to develop feelings for her, for antagonizing Michael. She watched as the two of them, now both werewolves, argue which eventually degraded into a fight.
She was turned by Brian after he stabbed her boyfriend Mike in a fight with a silver knife. Enraged, she uses her newly acquired werewolf powers to rip Brian apart. Kate spends her last moments before leaving a sheet over her boyfriend and leaving message for Sam and Dean asking them to give her a chance. She promises not to hurt anyone who is human and to only feed on animals. Sam and Dean ultimately decide not to kill her, and she is last seen walking away from a tractor trailer.
While tracking werewolf kills in Durham, Washington, Sam and Dean find and capture Kate who doesn't deny being the killer and dares them to kill her. As Dean is distracted by Sam, Kate brings out her claws to cut herself free. As she escapes, Sam and Dean find out that she is not the killer as there was another attack across town while she was with them.
After Sam and Dean track down the other werewolf and come under attack, Kate saves them and keeps them from killing the other werewolf who she reveals is her sister, Tasha. Kate explains that she hasn't killed anyone except Brian because he was crazy and that she is controlling what she is by eating animal hearts and using yoga and meditation. Kate shows them a silver knife she keeps on her in case she loses control like Brian so she can kill herself if that happens. Kate tells them that after leaving school, she went home, but couldn't bring herself to go in in case she harmed her family so she left to start a new life. After finding out that Tasha was fatally injured in a bad car accident, Kate visited her in the hospital and decided to turn her into a werewolf to heal her injuries and save her. Kate kidnapped Tasha who survived and explained what happened to her. However, Tasha embraced her werewolf side unlike Kate and went on a rampage. Kate insists she can control Tasha and asks for a chance. Dean claims they can cure Kate and Tasha if Kate leads them to her. Kate is dubious as there is no cure, but Dean claims one has been found. Kate happily agrees and tells them she will lead them to where they can find Tasha.
Kate leads Sam and Dean to her parents cabin where Dean handcuffs her to the Impala's steering wheel. Kate desperately pleads for Tasha's life as Sam and Dean arm themselves and head into the cabin. Kate manages to break free eventually only to find Tasha and two other werewolves holding Sam and Dean captive. Tasha explains the others are Brandon and Travis who she turned to be her pack and their new "family." Tasha demands that Kate either join the pack or leave but Kate refuses to leave or to kill Sam to join the pack. After the others leave the room, Kate tries to talk sense into her sister who proclaims that she is now a superhero and won't be walked all over anymore as she's now the one to be feared. Realizing that she's lost Tasha, Kate tells Tasha she loves her, hugs her and then kills her with her silver knife. Kate takes Tasha's matching bracelet and flees before Sam and Dean dispatch Brandon and Travis and come in.
At a truck stop, Kate calls her phone which Sam and Dean have and they agree to let her go again as long as she stays away from them and doesn't harm humans. Kate agrees, but can't promise as she now knows just how easy it is to lose control. Kate walks away down the road, alone once more.