Grace is only briefly mentioned in Allegiant.
When Tobias Eaton and Peter Hayes go to the Factionless' Headquarters (Old Erudite Headquarter) they are confronted by guns at the door. Grace who is among them recognises Tobias as they used to be neighbours in Abnegation. She hesitates to let them see Evelyn Johnson but after asking someone she lets them in.
Grace was Tobias's neighbour when he lived in Abnegation, she was described by Tobias as a nice person and he was surprised when he saw her with a gun as a Factionless.