Who is Macey McHenry from I'd Tell You I Love You, but Then I'd Have to Kill You and what is their importance?

Macey McHenry, known as Peacock during missions, is the daughter of a famous senator. Her parents want her to attend Gallagher Academy because they are out of options since she has been expelled from every other prep school for behavioral reasons. Cammie, Liz and Bex find Macey to be snobby, but when Headmistress Morgan decides to admit her to the school because of her connections and the fact that she is a descendent of Gilly Gallagher, the girls are expected to befriend Macey. Macey agrees to help Cammie learn about boys under the condition that Cammie helps her get out of the newbie class. Macey and Bex rescue Anna from Dillon at the pharmacy. Macey becomes one of Cammie's closest friends, and she is the only one who knows all of Cammie's secrets.