Who is CB's Sister from Dog Sees God: Confessions of a Teenage Blockhead and what is their importance?

CB's sister, Sally in the comic strip, dresses gothic in the play. During the funeral for CB's dog, CB and his Sally fight about who will say the prayer. She is angry at CB for kissing Beethoven because CB knows how she feels about Beethoven. CB's sister is devastated by Beethoven's suicide and tells her brother that she would have eventually accepted his relationship with Beethoven.