Skipper is Maggie's foil, because both are in love with Brick. Maggie tells Brick, "Skipper and I made love, if love you could call it, because it made both of us feel a little bit closer to you" (I.936-937). Both combat the frostiness and detached nature that characterize Brick, and both try to tell the truth around Brick (with frigid results). Both are love-starved.
Mae and Big Mama are also Maggie's foils as they are the reigning women who, in the world of Cat, have played society's role of "woman" impeccably well. Mae and Maggie both have names that start with the letter M, and they both come from families who were either poor to begin with or who eventually became poor. Both women know how to survive by climbing ladders. Maggie and Big Mama, while existing in vastly different eras with vastly different beliefs, are united by their unrequited love for their husbands. We hear both women convey their love to their husbands, resulting in the exact same response, "wouldn't it be funny if that was true?" The difference between the two women is that, while Big Mama dances around the truth and floats on a superficial stream of conversation, Maggie gets down and dirty with the truth.