She wouldn't. She's just obsessed with her sister and her form of "love" towards her sister is fucked up but later on she knows when to not cross boundaries and try to be with her sister in a much healthier way. She loves her sister even more than her parents, it's just she doesn't know how to show it a not fucked up way. She'll soon later on know how to respect and accept that her sister is her own person and she will then leave the north because for her sister's sake. She's actually gonna bully blondie of what she did to her sister.
Her clarification and redemption is more believable than so many other stories.
Yes. This is what I believe so as well. Her love, obsessiveness to the FL is yandere type. A toxic relationship with the sister. But, fortunately enough, you spoiled that she will learn later on. I might curse that sister multiple times before.
At least we don't have another blondie going crazy for the duke, if redhead started to like the duke I would've went ballistic.