Except she wasn't. Federal law, the Americans with Disabilities Act, supercedes state law and definitely school district policies. ADA allows people to not wear masks when they, as the police admitted, have a disability.
The basis for the arrest is about as lame as arresting a blind person with a seeing eye dog because the school prohibits dogs on their property.
So, for the sake of argument, assuming she was exempt under the Americans with Disabilities Act, and the police were ultimately wrong to arrest her (presumably she had explained that exemption to the officers as opposed to just asserting she was entitled to disregard the facility's posted policy)... does the Americans with Disabilities Act entitle her to resist arrest?