Sit down together and write terms of friendship and nobody will break these rules.
1) Never say or do anything which hurt other person.
2) Trust your friend and never break the trust of other person.
3) Defend your friend in her absence.
4) If she is angry and say something witch you do not like, forgive her.
5) Never fight in front of the class or other people.
6) Sit together and find out the solution of the problem.
7) Always try to speck truth.
8) Never blame each other.
Any thin else you can add.
This exercise will help you in latter life as well.