Unions usually support the employee when they appeal job actions like dismissals, not criminal charges. If the employee has legal coverage through a union sponsored insurance program her coverage can come from that, otherwise she hires a defense attorney.
If she is not found guilty, she could come back to the union and appeal for her job, but the district can fire her even though she was found not guilty in court. Different standard of evidence.
Yes.
After doing "community service" for her temporary lapse in judgement, she will be promoted to a higher paying, less stressful job. Very likely, she will be the principal's boss.