Little is known about Karla's past other than she worked in some kind of medical lab with her abusive boyfriend. She wanted to "protect" herself from him so she had razor blades permanently grafted onto her finger tips. However, her boyfriend wasn't her only victim and it was hinted at that she became a serial killer.
Fight On Edit
In "One of Us", Cal comes to Karla's apartment and removes her shackles. He then offer her the opportunity to get revenge on S.H.I.E.L.D. and show the whole world what S.H.I.E.L.D. does to enhanced people like them. Karla agreed and went with Cal and the others to Brynmore Psychiatric Hospital to free Angar. During the break out, Karla slit the throat of a security guard.
Cal next led his team to Mantiowoc, Wisconsin, Coulson's home town, ensuring Karla and the others that S.H.I.E.L.D. would come to them. After Karla and the others attack a local high school, Coulson and his team do appear. However, right in the middle of a stand-off, Gordon teleports in and grabs Cal before teleporting out.
Karla fights Bobbie, but Bobbie defeats Karla who is presumably taken to prison later.