leah's position within the family unit as a daughter-wife, rather than just a wife (whether this is acknowledged or not) makes her hate for mercy much more sensible than people give her credit for. the violent and excessive nature of her reactions towards mercy since she was a child could have other explanations (who knows, i'm all for alternative interpretations), but i think it works fine when taking into account that being jealous of mercy being cherished as a daughter is part and parcel with being jealous of her as a potential lover. which is not to say this was leah's conscious thought process. i don't think she sees herself as bran's daughter. i just think by nature of how she was brought into the fold, a young girl being raised under bran's tutelage reads as someone filling her exact role. and doing it better! mercy is loved! being bran's wife and bran's "daughter" are not discrete issues for leah, as someone that was raised to be his wife. in this sense, i think she would have projected sexual jealousy and expected that bran would develop a sexual attachment to mercy regardless of his actual feelings, simply because it fits the framework she was given for his behaviour. the fact no one apart from her and bran knew the truth of her turning and that they likely were the only ones having an inkling of the scope of bran's feelings for mercy when she was still a teenager does not seem incidental. leah knows for certain that bran has both the capacity and the inclination to blur the lines between charge and lover and take advantage of someone dependent on him to extract what he needs out of them. or at least the only one that knows this exploitation can entail a sexual component when directed at a female subject.
leah has no one else in the world and her role as bran's mate is her only claim to economic stability and a measure of acceptance and respect, if not love, in life. additionally, she was (re-)created by bran in such a way that her identity, abilities, and whole existence have a use only in relation to him. if she loses him, she does not have anything, not even herself. and since bran does not love her (or so he has made her believe), she cannot try to influence him in order to keep her position. i am not saying her treatment of mercy was right, especially as i am not particularly interested in analysing characters from a moralising standpoint. but i do think it was rational, insofar as in her view the removal of mercy from bran's life was actually the only thing she had the power to affect to ensure she was not abandoned. the only option over which she could exert some control.
what is extremely sad to me is that however much leah may be relieved that bran doesn't finally act on his attraction to mercy (and justly so! it would be the ultimate cruelty for bran to create her, use her, and then also leave her!), the fact he sees the harm he would inflict on mercy by pursuing her and decides to spare her, while he had no problem inflicting that same harm on leah, works as a further confirmation that mercy is in some way better loved. that she is allowed to be seen as a whole person, to grow as an independent being without being crushed under bran's weight. as we have very little of leah's pov, i am not sure whether this thought has ever crossed her mind, but it has certainly crossed mine very often.
