Dark MagdalenaMy question is, when my best friend comes up again, what do I say to my mom? FWIW, my mom is a medical doctor; she knows the signs of mental abuse and knows that it is real. I have no idea why she suddenly thinks that this is a matter of simply growing up instead of a response to mental abuse.
Why would your friend come up again? Will your mom ask about her? That was common enough with my mom. We knew each others friends and took an interest in them, so that seems natural enough to me. If it would be you bringing her up, then think about not doing it and saving yourself the aggravation.
Appeal to her medical expertise. Ask her why, as a medical doctor, she thinks it's immaturity rather than emotional abuse. Question her about the signs that you've seen that seem to fit emotional abuse. Why does she think they don't apply in this case? Get her into her professional pattern of thinking and see if her opinion changes.