Wiccans, please help?

A couple years ago, my mom and her friend who is/was wiccan (i'll call her Dana), were in a conflict involving Dana sleeping with my moms boyfriend (who have broken up). But to the point. what is "the law of thre"? My mom and Dana were having an arguement using text messages and what stuck with me, cause i thought it was funny, was when Dana sent a message saying "I now invoke the law of thre" to which my mom replied "learn how to spell before you cast one." Maybe she meant "thre" but i looked it up and found something which essentially means what you do to others is returned threefold. if this was the spell then why would she cast it if she was caught with my moms boyfriend?