My money is she knows that Serina is going to lose her scholarship, hence why she’s sleeping with women, for probably money. And I bet the reason why she can’t let herself be #2 to help Serina out is just a simple and not-complicated demand by her parents or something so she just helps her by giving money. She probably also likes her to which is why she picks on her, probably just doesn’t know how to talk to her either.
Honestly, they’re both kind of dumb really despite being the top 2, which goes to show book smart /= street smarts, because one of them should’ve been a little more careful if she was going to work that kind of job, and also she really needs to tone down the arrogance, yeah she’s talented but she’s gonna fall hard when she meets someone even better, and the other one probably should’ve prepared for her plan backfiring or some sort of pushback from the other person, and also that blackmailing Reiko in order to win is just admitting that she isn’t as good at Reiko, who I think we should admire for her time management skills at the very least, #1 student, student council and disciplinary member, and a club helper and she still has the time to be a part time love machine.