Maev is the leader of a band of female warriors known as the Free Hawks who help Saba bust out of jail in Hopetown. She ends up doing something a lot more important than that, however: she becomes Saba's first real friend.
These two warriors grow close while taking sanctuary in Darktrees, Free Hawk HQ. Saba is a distrustful person by nature, so she's hesitant to accept Maev's generosity. Maev, on the other hand, won't take no for an answer. She continues to show her hospitality, providing a sounding board for ideas and giving advice, and in the end she proves herself to be a true friend. Just look at her response when Saba promises to pay her back for her kindness, for example: "Friends don't owe, friends don't repay" (7.249).
During the novel's closing battle, Maev and the Free Hawks show up at the last second to save Saba and company from the clutches of the Tonton. That's true friendship. We're not sure what's next for Maev, but we're confident she'll cross paths with the Angel of Death in the near future.