This article isn’t clear about what Norton actually did. Another article has more information.

Still, Hixon said, Norton put the district in a legally difficult spot by falsely attesting her child was born female on her state athletic eligibility form. The Florida athletic association fined Monarch $16,500 for violating the act, put the school on probation, and the district could be sued under the act if another student believes she was kept off the volleyball team and lost scholarship opportunities because of Norton’s daughter.

As far as I can tell, Norton didn’t break the law since the law only restricts public schools, not students or their parents. What isn’t clear to me is why the school was punished, since the law states

© Athletic teams or sports designated for females, women, or girls may not be open to students of the male sex.

(d) For purposes of this section, a statement of a student’s biological sex on the student’s official birth certificate is considered to have correctly stated the student’s biological sex at birth if the statement was filed at or near the time of the student’s birth.

The school’s official policy didn’t violate the law, but I suppose that the school was punished anyway because it is responsible for the actions of its employees and as an employee, Norton had a responsibility to report rule violations. The fact that the student violating the rule was her own child was not directly relevant.

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I don’t have an issue with this.