You can wear a hijab if you want. no one is stopping you.The more we shield Muslims from adhering to the same standards and being subject to the same rules as everybody else, the longer integration & reform of Islam takes.
She can wear whatever she wants to please her husband/parents/friends/teacher, but nobody else is allowed to wear random head-dresses in this particular sport - it has rules. If you can't make the "choice" to just not wear it for one activity, then don't take part.
There's the rub, though: Hijab is not simply "a choice". That's just a lie white liberals and western Muslim women tell so they can make excuses for Islam. If it were then there wouldn't be such strict adherence to the practice and special pleading surrounding it. Almost like indoctrination is powerful, almost like they don't really have a choice.