Yes, that’s an interesting point. Perhaps the change in Marina’s character is more compelling precisely because she started out so passive.
I would have liked to see how her relationship with Mr. Fox changed, because I didn’t really get a sense of it when he visited the jungle. If Marina had started thinking of him as Jim towards the end, I would have felt like she was in a position to change the power dynamic there. As it was, I got the impression that she might just slip back into her deferential ’employee’ role in their relationship.