What is the importance of Matilda's and Lavender's friendship and why?

Lavender is one of Matilda’s new-found friends in her school. She is extremely small for her age, and has deep brown eyes and a fringe. Much like Matilda, she is very brave and mischievous. She plans an elaborate prank on the Trunchbull that is very successful. Matilda needs this fiendship in her very isolated world.