Elaborating on this post!
I'm sure other people have written stuff like this but for a post book 3 fic or drabble I'd like to explore Grace traveling the train on her own after all the Apex kids have left. Mostly because I want to see her interactions with denizens, both ones that allow her to have a clean slate, and others that she'd hurt in the past.
It probably would not be Hazel though because I feel like while I do think Grace should make it up to Hazel somehow I still think it's a bit too soon for Grace to be majorly in Hazel's life again. I don't think she's necessarily better off with Amelia but that's a conversation for a different post.
It's hard to explain but I feel like once your identity as someone considered an "outsider" to people who are supposed to care about you and protect you gets exploited for their benefit, it's hard to come back to that trust with the person who threw you under the bus.
What I'd want to have in canon vs what makes narrative and thematic sense are at odds because what I'd want would very much undercut the lesson Grace was supposed to learn irt Hazel!
I say it's different with Hazel vs other denizens Grace hurt because Hazel was one of the only denizens Grace formed an emotional bond with. So her hurt and betrayal is more personal and Hazel still needs time and space to heal from that before she's ready to trust Grace again. Could be a couple more years, could be decades, could be never. I think Grace would respect that.
Of course, again, that's not to say other denizens have more of a reason to forgive or trust Grace because she never connected with them.
Out of any denizen I'd love for Grace to interact with post canon is Kez. I promise I am not saying this out of my biased love for Kez. I feel like while she didn't go to the extremes as Grace did, she knows what it's like to hurt people unintentionally, even if it was in the name of the greater good she believed in. I think she'd be the most understanding of Grace's past if she opened up to her (which I think she would after a while).
I was also gonna say that maybe Grace could try helping the turtle citizens of the unfinished car as a way to make amends with previous denizens she'd interacted with but I remembered it was ejected and in quarantine so. RIP.