Glória is Macabéa's coworker and rival in the competition for Olímpico. (That's one of those fights where, when you win, you still lose.)
Actually, there was never really any competition at all. When Olímpico "set eyes on Glória, Macabéa's workmate, he felt at once that here was a girl with real class" (4.276). This is because Glória is light-skinned, swings her hips when she walks, and proudly claims to be "carioca," which means she's from "the privileged class who inhabited Southern Brazil" (4.277). (Check out "Character Clues" to learn more about class.)
Glória isn't particularly pretty, but she is well-nourished—in other words, she's got curves and confidence. She would "[wiggle] her bottom in an inviting way and she smoked mentholated cigarettes to keep her breath fresh for those interminable kissing sessions with Olímpico" (4.316). Okay, gross, but it seems to work for Olímpico.
It's hard to say, though, whether Olímpico is more attracted to her body or her social position. One of the things he find most appealing is that she has both a mother and a father, and she eats "a hot meal at the same hour every day" (4.279). (See, this actually helps us feel sorry for Olímpico, because you get a sense of how deprived he must have been to think that these things are luxuries.)
But just when you want to hate Glória for being a boyfriend-stealer, it turns out that she's the only one who's actually nice to Macabéa. She invites Macabéa to her house for tea; she lends her aspirin; she recommends going to a doctor; and she suggests visiting the fortuneteller. Not exactly BFF material, but still maybe the closest thing that Macabéa has to a friend.