I don't know of any high schools that do teach proper stage management at a professional level. I ASM'd for the first time as a freshman in college with no stage management experience and I learned. My SM, my director, designers and other stage managers in the department taught me things and I learned. So I wouldn't complain about how your ASM doesn't know anything. If I were you, I'd have her shadow me and I would teach her in the process. Honestly, having an assistant is about training them to do your job, is it not? So, this is technically your responsibility to make sure she learns the things she needs.