Maggie Ziff is an alternate version of Maggie. She would have been the daughter of Marge Ziff and Artie Ziff if Marge had married Artie instead of Homer.
History
Bart goes back in time and stops Homer and Marge from becoming a couple when he realizes if he does that, he will be rich. He goes to his new home, a mansion and sees his two sisters slightly different with curly hair.