While on an extermination mission, Claudia finds her 8 yr old brother orphaned and marked for death. She defects to get him to a rumored safe haven if they can make it? in time. Big thanks to Cynosurer for the feedback

"Extermination mission" makes Claudia sound like the bad guy. In fact, she is the bad guy! Presumably in the screenplay, she realises the error of her ways, but since you won't have room for that in the logline, could you make her mission sound more sympathetic?

This is still a bit rough in the middle but I think you see what I am going for:

"When her younger brother is marked for death, a resistance fighter must desert her mission and flee with her sibling to a safe haven before they are tracked down and killed."

While her goal is clear, I don't see what sacrifice she is making to achieve it.