She would never do this to him. Saying this kind of just shows you don't understand her character. She would have his back through anything. Interesting you interpreted her this way. Multiple times she praises his selflessness and good qualities. It is just playful mockery. If anything she is jealous in a way of how much of a good guy he is, cause she sees herself negatively as a murderer.
She knows how he feels about his injury (or she should if she actually cared), so she spars with him alone, she somehow gets the better of him (ex military and current pro MMA), puts him into an armbar on his injured shoulder and doesn't let go until Valentine steps in, then she's surprised he storms out of the gym.
She doesn't praise his selflessnes, because (at least at this stage) she doesn't truly believe that's a positive trait, it's a trait that leads to loss.
Is not like she doesn't like him, she likes him like she could like a good loyal puppy (which to be fair to her... he is a bit).
Also the 2 don't have real banter, banter is back and forth, when one of the 2 always gets the last word it stops being banter and becomes making fun of, not saying it's unusual, just saying that if you are actual friends (and not just buddies) that's not how to go about it.
Btw I'm not saying she's a badly written character, quite the opposite, she's a bit "stereotypical" in her own way, her main defining trait being the trauma, her secondary one being her barely contained feeling of unjustified superiority (upbringing + natural gifts), her goal is to find someone who's "as bad" as her with whom to share, and either come out of it or dwell in it together.
She's torn between feeling guilty for her privileges and being guilty for what she did, and what "stops" her is the fact both things she feels guilt about are caused by her being a winning and dominant personality.
