She is the sister of Vernon Dursley. She is unplayable in some versions of the game, but is playable in the PSP and DS versions of the game. Harry gets so mad at Marjorie that he accidentally inflates her like a balloon.
Her hair is similar to Willie Scott's (Party Dress), but it is an orangish brown instead of blonde.
In The Video Game
In the game, when Marge inflates, her finger (or LEGO hand) touches Vernon's fork, causing Marge to fly everywhere just like a what a real balloon would've done if it hit a fork. She is only playable on the PSP and Nintendo DS (portable versions).