I'm in the US (not Florida) and the BBC have missed a few contextual details on this story.
First of all, Tallahassee Classical School is a private school which markets itself as conservative and has its own set of internal rules. I'm not sure why the BBC is linking this story with the bill being debated in the Florida Senate, which applies to public (state) schools only.
It was the school's own rules that required that the lesson that included Michelangelo be preceded by a notification to parents. Hope Carrasquilla, the Principal who resigned, agreed that the procedure was not followed and took responsibility for the failure. The School Board Chair who asked for Carrasquilla's resignation said that there had been multiple issues with her performing her job duties and declined to comment further based on legal advice (which is sensible in this case as Carrasquilla may bring a lawsuit for constructive dismissal).
So yes, the standards of the school are peculiar and not typical of a US public school, but it's not clear that the request for Carrasquilla to resign was inappropriate.