The Junior B team in my town just named a woman, Abbi Vigue, as assistant coach. The post is pretty much a volunteer position here (which has to do with a former owner pocketing a bunch of cash, leaving the current guy with big debts to pay off) so they usually find someone local who can spare the time and who knows a thing or two about hockey. She played for the B.C. provincial team and at the NCAA level.
That said, I can't find any mentions of any women coaching junior hockey, even as an assistant. Has it happened before?