At a popular theme park, a new dancer/actor secretly experiences grief and rivalry from the other females in the show as she tries to fit in as the new girl, and survive as slowly employees are disappearing and no one knows why.

thanks guys for the input !

Due to time zones DPG and Richiev posted my exact thoughts before I had the chance to.

I would make it more personal and specify the inciting incident more:

After her only friend is mysteriously killed an unpopular shy dancer at a busy theme park must find the murderer before more are killed and she becomes his next victim.

Hope this helps.

"grief and rivalry from the other females as she tries to fit in" = "unpopular", lopping off 11 words from the logline. That's she unpopular implies she's not fitting in and suffering emotionally.