She is realistic in this way, a pretty girl like her would have lots of options... and wouldn't become obsessed with the first guy she met.People really don't get she's just a female version of MC? She's new to school and trying to figure out where she fits in. She's playing the field like MC. She flirts her and there, just like MC. If the player is on her path they can get her to commit to MC. The whole story of her path leads to that. There're four paths at the moment: the one where she falls for MC, the one where she's crushing on him but don't act further, the one where she's just friend with him, and the one where she dislike MC because of the way he acts with girls generally (cheating, peeping, etc.) It's on the player which path it is with her.
Her romance path has been slow to progress(i'm not calling it bad writing or unrealistic, just calling what i see), she keeps her cards in her pocket and hasn't committed to anything thus far.
The upcoming beach date is pretty much the first thing we do with her without any pretense of being anything other than a date(other times were under the guise of "training").
So while i don't really think it's bad writing or anything, i can understand people who criticize "why is she so distant?"