If  ever there is no third party just to mediate the parent and the child , no need to have another person to resolve any arguments between them. It is a family problem and who ever intervene if he is not a member of the family, he may be called as an intruder.

 I think it is not proper to have a third party. I agree with , Warren.

a third party may be needed if the two dont communicate or if they get violent a third person perspective or intervention may be needed at times like this. 

A mediator is needed if the parties are unwilling to talk or negotioate.  Sad to say, in some families, they are needed. 

In my school, a guidance counselor had to act as mediator between my classmate and her parents.  The girl (classmate) was becoming a junkie and the class sl*t!  I dunno how effective it was since it was a closed session but my classmate is doing better.

Im so glad for your friend.  It can be tough on girls who want to become popular.  they are sometimes victimized because of this.