Ladies and gentlemen, meet the wicked stepmothers.
Oh, except she's not wicked.
But she is Lauren's stepmother. Cory's native language is Spanish (1.13), she plays piano (5.5), and she teaches the kids of the neighborhood (3.39). Seems pretty cool, right? Yeah, for Lauren, she kind of serves as another role model of a community leader, just like her husband Reverend Olamina. When Lauren wants Amy, the poor girl no one cares about, to start school early, Cory says sure, so long as our narrator takes charge of her (4.13). That's an example of how Cory keeps Lauren thinking in terms of responsibilities and work.
There are some downsides to Cory, though. According to Lauren, Cory favors Keith over the other Olamina kids—"Keith is Cory's favorite" (8.49). The favoritism basically continues despite Keith running away from home several times, a habit that eventually gets him killed. Maybe the favoritism is one reason Cory barely enters Lauren's mind—only once or twice—once Robledo is destroyed and she migrates north.
Once Lauren has reached Bankole's land, she does think back to Cory briefly. Regarding her time in Robledo, Lauren thinks: "I think I was into my own brand of denial, as bad in its way as Cory's or Joanne's mother's" (25.15). So Cory, for all her upsides, represents more Robledo-style denial for Lauren. Like Lauren's father, Cory, one of the adult leaders of Robledo, didn't see the trouble coming as clearly as Lauren did.
Don't forget the argument between Reverend Olamina and Cory that Lauren overhears in Chapter 6. That's when Cory's trying to talk Lauren's father out of the night patrols, saying they're just going to get him in trouble. This conversation is an example of the denial Lauren later thinks about. At least Reverend Olamina wanted to solve problems in Robledo; Cory was having a hard time acknowledging the existence of any problems.
Nevertheless, when Lauren's father goes missing, Cory really steps up to the plate, taking over his university job in some way that's not quite legal (13.100). So she does her best, it seems. That's just not good enough, of course, in the face of the change that's coming: Robledo is going down, and Cory and Lauren are just going to be separated for the rest of the book.