Totally agree with Katrina. The issue is that there will be people like J in C's life when she is older. J could be a boss, client, colleague or even neighbour. It is helpful that she learns how to work and relate to those people with boundaries. I am not saying that 12 is a correct age to deal with self-harming friends but it is better than C learning at 21 that she has no clue dealing with difficult friends.