Of "the favorite subject myself", Mildred says, "I understand that one "how does this show a contrast to her foil, Clarisse?

This illustrates how self-absorbed and superficial Mildred is. Clarisse thinks of other people, she is empathetic to other people's feelings. Mildred is caught up in herself, she can't think past her immediate wants and needs. Both Clarisse and Mildred are opposites who bring out each other's personality.