Cameron, in the Sarah Connor Chronicles, played by Summer Glau, is the ultimate girl with a gun. Except that she is not a girl, not really, but a machine. As such, she shouldn't have any emotions... shouldn't have. But she is John Connor's protector, and she'll do anything, even die, if it will keep him alive.
But even a machine has a dark side, and since Cameron was once engineered to anihilate the human race, not protect it, there could be something nefarious left in her memory that could awake at any time. Is she the heroine who will save the day? Or the perfect instrument to destroy the human race?
She is aware of it. John is aware of it.
But boy is she a model of efficiency when it comes to getting the job done.
Personally, I think Cameron is evolving into a sentient being, more sensitive than she thinks she is. And I believe she has feelings for John. Whether such a relationship has any chance to fly, your guess is as good as mine.
Girls with Guns, Romance with a Kick