Also going to posit that "not fond of this person because it feels like they took her brother away" may indeed be the reason for her frosty demeanor.
...In that the sibling she spent time with, admires, and relied on suddenly had much less time for her. Even less after he moved out. Which, shockingly to some people, is normal. You can be jealous of someone getting a family member's attention without being sexually attracted to said family member.
Insert trope from every sitcom ever where the [child] gets jealous because their [parent] seems to prefer [other person and/or relative] in some way. You guys cry incest over those scenes too?
...In that the sibling she spent time with, admires, and relied on suddenly had much less time for her. Even less after he moved out. Which, shockingly to some people, is normal. You can be jealous of someone getting a family member's attention without being sexually attracted to said family member.
Insert trope from every sitcom ever where the [child] gets jealous because their [parent] seems to prefer [other person and/or relative] in some way. You guys cry incest over those scenes too?