My 10 year old daughter has temper troubles and behaves very rudely with my girlfriend. how do I find out what’s wrong?

Communication and bonding will be helpful. Look for activities which your child likes and plan for an outing as a family. The activity maybe able to ease the tension and cold silence, If there is no bond, there will be no respect or anything else. Your girl needs reassurance, and its our job to protect, love and nuture them to a beautiful lady in time to come.