I actually like this, could definitely use a sequel. Seems like she knows her childhood friend doesn’t view the “little sister” as anything more than a formality and plans to just dominate her time elsewhere. Also seems like she’s been dominating her time at school too, which is why the “little sister” is complaining and asking to see her for lunch.
Does make me wonder if you can change sisters. I can’t imagine they would force you to stay with someone if you don’t get along.