A cute blush is not enough to redeem the black-haired girl. She's like a three-year-old who hates their younger sibling for the sin of being born, without the excuse of age.
You know, she didn't actually hurt her or anything? All those requests and a shitty attitude - she was just an asshole to her sister, not a real bully. Blonde didn't have to listen to all this crap and nod. But she did. Not because she was afraid or forced, but because she was fine with it. So I can't see why all the blame goes to the big sister. You know this shitty statement that it's a victim's fault for being bullied? It's bullshit, but in this situation it makes maybe just a little sense. Besides it is clearly stated that she didn't actually hate her new sister, she was just sad for her mother. Which is understandable, I guess. So it's rather tasteless comparing her situation to a 3-year-old's tantrum.
Can't really see the blonde's chipper personality as anything but a facade; the infatuation comes off as a weird form of emotionally misdirected Stockholm syndrome instead of anything approaching love.
I don't believe it's a facade. Actually I think she's one of the most honest characters in a while. Remember that page, when she was introduced to her new family? She was with her mother, all in bruises with dead eyes on her face? I assume her previous family was a life of physical and emotional abuse. And after that hell she was introduced to her new family. A family that wasn't all sweet and shiny, yes, but she could see that they were good people and it was a new warmth that she hasn't previously felt. It may seem weird from a normal person's perspective, but to her...she was just glad.