Aaand her step-sister is MC's homophobic* ex. It's a bit predictable...
Also, that friend is giving me the chills, I'm sensing some major yandere vibes from her.
*Let me correct myself, she might just be asexual and saying that it was disgusting might have just been an aversion to sex. I have no idea how people experiencing asexuality feel towards doing it with their partner (someone who they are romantically involved with) but it seems some are ok with doing it (but not necessarily trilled about it) while for others if the s/o pushes it, it becomes a deal-breaker.
I still wonder how she'll react when she finds out the (girl) friend she ghosted and probably invokes some trauma (it is the first person who expressed explicit sexual interest in her, a thing which she finds unpleasant) is now friends with her little sister...
Some people are saying she could have been romantically attracted to MC but she could as well be aro, so in the end she feels nothing but apathy for "that girl who she dated in HS". So I'm betting on some extreme reactions, instead of having mixed feelings and perhaps being jealous. She will probably tell Azuki to stay away from her sister. And if she finds out the sister's secret she might even acuse the older girl of being the bad influence.