Noun: The arch rival and nemesis of Ballsy Marge. She was made to balance the world. Without Sweet, Sweet Heidi, Ballsy Marge would be able to roam rampant and free. Sweet, Sweet Heidi is the archetype of everything that is good and altruistic (and she's probably ridiculously hot).
God, I'm glad Sweet, Sweet Heidi is here to make the party better. Ballsy Marge was being a bitch and flipping tables over and hitting everyone in the nuts.