Hi Edge, I've got some ideas for other characters, this of course being a long term thing.
For some reason WTS seemed to focus on making Cho hermiones rival (they wouldn't have any crossover, Hermiones a book worm, and cho's a jock, they honestly would never meet); But rival wise in this game you could have it be Tracey Davis and Daphne Greengrass for Slytherin; the Patil twins (saves on art, to be honest) for Ravenclaw and Gryffindor; & potentially adding in Lavender Brown whos looking for affection after leaving Ron.
Otherwise you could stick with the good ol' Pansy, who Hermione actively despises, and who she'd eagerly wish to corrupt after you've reached a certain threshold.
Otherwise there is the old regulars...
Luna's an old favourite but she has been done to death; Susan 'exists' but overall is as neglected as Harry in his cupboard; & tonks... People just get stuck on tonks, don't ask me why.
Alternately, since you've played around with Snape, you could potentially have the rest of the golden trio be genderswapped; or get genderswapped, after they try to confront us when Hermiones reached a certain threshold.
Regardless, best of luck. We will watch your career with great interest!