Yeah I can't get a good feel for her character or if she even actually did anything. Wouldn't be the first series that had this premise then later say it was all a rumor.
Opening about her doing it with the first dude was very vague and ambiguous, I feel like you'd want to be more clear on something that's supposed to be your central premise and establish your character.
Why is she acting so desperate to go out with this dude if she has so many others?
If she's charismatic to the point of getting all these dudes why doesn't she have any friends? I get that some of the girls are angry at her but still seems inconsistent.
Why is she acting so snarky about having sex with someone else's boyfriend, looseness aside, it's objectively pretty sleazy to knowingly be an accomplice to cheating, if it was true the other girl is justified in being angry.
She seems to have a pretty idealized view of romance (calling him a prince, getting embarrassed easily, etc.) for someone who is seemingly experienced.
Guess the idea could be that she had been playing around but wants a more serious relationship now? Just not really feeling it from the way she's portrayed.
If I had to bet i'd say it'll turn out to be a rumor that she played along with for whatever reason.