No one is keeping her from competing except her. She can follow the technical rules and compete this afternoon. The singlet rule is obviously designed to allow the judges to see her elbows, knees, and buttocks so that her compliance with the technical rules can be evaluated. Muslim women are free to compete just like every other person that wants to comply with the established technical rules of the sport.
But I don't think that's your question. You want to know why we should make a person who doesn't wish to follow the rules if they offend her sensibilities follow them anyway. Right?