Maggie, "the kitchen woman with legs like parentheses," is a target of violence and scorn for the "gar-girls" at St. Bonny's. Maggie is significant because she is racially ambiguous--she is "sand-colored" but Roberta calls her "black" while Twyla does not think of her as such.
This story is all about racial stereotypes. By making both Twyla and Roberta a "mix" of black and white stereotypes, Morrison deliberately makes it impossible for the reader to determine which girl is white and which is black--just as Maggie's race can not be determined. While it is race that tears the two friends apart, the differences between them are so unclear that the reader does not even know which is which.
Like the two younger girls, Maggie is mistreated and Maggie is racially ambiguous. When Roberta says, "What the hell happened to Maggie?" at the end of the story, she is, in some way, also asking, "What the hell happened to us?"