Fandom: Agents of S.H.I.E.L.D. (Marvel)
Jennifer, or Jennie, is one of the main team. She goes by her mother's last name because she kind of hates her dad - Agent Garrett - the main Hydra guy who recruited Ward.
When Hydra starts to take over, she plays along with her Dad before turning on him and helping the team escape and rebuild S.H.I.E.L.D.
The reason she hates her Dad so much is because he used her as a "lab rat." He tested Hydra's attempts to recreate the super soldier serum on her, which almost killed her on several occasions. The side effect is that she has greater physical strength/capability than the average person. Also, if she gets too worked up or exerts herself too much, her body starts to "overheat." (Kind of like the guys in Iron Man 3. My thought is Hydra's serum was based off extremis since it's the closest anyone has come to recreating the super soldier serum.)
In season 4, she works with Ghost Rider. She understands him a bit better than the others, having to deal with a power she didn't want or ask for and has sometimes seemed to cause more bad than good.
In The Framework, her reality is that the serum worked, but was too dangerous to give to anyone else. She's an enhanced agent of the underground S.H.I.E.L.D. and sacrifices herself so the others can escape.
A/N
I killed her off because, IMO, the next seasons get a little weird. Not to mention that the whole time travel thing in season 5 doesn't work with how Loki explains the timeline functioning.