print out some key pages on this particular group, then print out a couple others, then go to the head of the school again and tell her what happened, but also explain to her how the teacher’s question opened the door on it.
Another option is to memorize a few links that show the problems with this MLM, or have them printed out on small pieces of paper, even blank business cards would do. When she does that in front of the class again, if she mentions the company name, wait until she finishes, raise your hand and *politely* mention that you’ve researched the company and that there are many experts consider it a pyramid plan (don’t say scheme, that’s too offensive). You can add you have experiences with them if it fits and even say you’ve got links for those that don’t believe you. This would have to be done VERY gently.
It would turn this woman against you, but she’s a drone, so you knew that could happen. If this happens a few times, she might realize that just mentioning her company will invoke a response that it’s a pyramid plan and might realize that at least around you she should shut up.