Absolutely the student did wrong, and should be made to face some sort of consequence for stealing his teacher’s smartphone and then accessing and distributing her personal [nude] photos on it. And, I agree that the school system was way out of line for condemning her, if [as it appears] they rushed to a judgment of her without simultaneously investigating and determining how to address the student’s actions. (They’ve ducked the issue by saying his fate is being left up to Law Enforcement.)
The deeper question is this: how responsible is the content owner (the teacher) for creating and retaining such content, and then making it accessible – even if inadvertently or illicitly – by others? Does an expectation of privacy prevail, as she claims?