Who is Hortensia from Matilda and what is their importance?

Hortensia is present in only one scene in the novel, which takes place on Matilda's third day of school in the playground. She and Lavender are approached by "a rugged ten-year-old girl with a boil on her nose" (pg. 102.) This is Hortensia, and she tells Matilda and Lavender all about Miss Trunchbull and the battle between the Headmistress and the students. She also talks about her own efforts in the battle, which involve syrup on a chair and itching powder in knickers. Matilda and Lavender are impressed and inspired by the older girl and promise to help in any way they can.