It reminds me of The Incredibles where the boy wasn't allowed to compete because he's so much faster than everyone and has to hide his ability. At the end when he is allowed to compete, he is told to only barely win; to downplay his capabilities.
The "barely win" thing is solely about preserving the family secret. It doesn't make the race any more interesting. I can only imagine that they're hoping he'll get bored after winning a few plastic trophies and go off in search of something more challenging.
That's not really the case here. She's not categorically different from the other female athletes. She's slightly stronger, slightly more talented, and slightly bolder. In sports, such slight advantages mean consistent wins, but only if you work as hard as everybody else. They're not magic.
She's not being held back to protect a secret. She's being held back because of a murky set of biases, resentments, and politics.