Enemies of the Heir
During second year, Ginny Weasley inexplicably wants to befriend Delphi. But she seems to be going out of her way to avoid Ron and especially Harry, which should eventually strike Delphi as weird verging on suspicious. Ginny seems to have a completely different personality around Delphi than around anyone else, and the last time that happened, the motherfucker had Voldemort living in the back of his damn head.
All the "freeing Dobby" and "Hermione starts S.P.E.W." stuff should probably happen during second year (or possibly third). The gist should be that Hermione finds out about Hogwarts's elves a few years early and immediately begins her crusade against their enslavement; Delphi isn't really here for that shit, but she does start to pay more attention to Dobby's suffering. Eventually, she outright asks Dobby about what he actually wants his life to be like, and when she hears his lofty ideas about freedom and employment, she sets herself to the task. So she musters up the courage to ask Dumbledore about employing him at Hogwarts and then comes up with a plan. Ideally, this should involve faking Dobby's death so that the Malfoys won't know for sure that Delphi had anything to do with what happened.
Because Dobby never gets involved in the diary plot, the entrance to platform 9 3/4 never seals on Harry and Ron. That means they never take the car, crash into the Whomping Willow, or break Ron's wand.
When Delphi discovers that Harry speaks Parseltongue, she's stunned--and ecstatic. They have their own private language now, something that only the two of them share. (And so Delphi walks away from the only meeting of the dueling club with the beginnings a crush on both Harry and Snape.)
After Harry is outed as a Parselmouth, Draco spills the beans to the other Slytherins that Delphi is, too.
After the attack immediately preceding Hermione and Penelope's (or Justin and Nick's?), Delphi goes to Snape to ask for an audience with Dumbledore. As she's spilling the beans on the mysterious voice that only she and Harry can hear, the reason that only they can hear it finally clicks: it's a fucking snake. There's a goddamn snake sneaking around the school! But if it's Slytherin's monster--and of course it must be--how are they going to find the Chamber of Secrets? And who is the Heir of Slytherin? (Dumbledore, of course, almost certainly already knows all of this... But he's impressed with Delphi's realization and pleasantly surprised by her confession nonetheless.)
When Delphi realizes that it's a basilisk, she (with some help from the twins) begins looking into Colin's camera and how it could possibly have saved him. What she finds is that the refraction method of the camera worked as a mirror and saved him, and she and the twins make a prototype for basilisk-safe glasses. Looking into the camera is what prompts her to take Muggle Studies.
As an Enemies of the Heir side note, it's worth pointing out that Harry refers to Tom Riddle as "attractive" many more times than he does in regards to any other character (including Fleur, whose beauty is literally supernaturally enhanced). As such, I think it can be assumed that Voldemort was objectively an extremely good-looking young man; within the confines of this fic, however, I'll be using it as early foreshadowing of Harry's bisexuality. He (privately) thinks Tom Riddle's hot af (and hopefully refers to him as "handsome" and the like a few times aloud, potentially clueing Delphi in on his genuine attraction), which leads to him noticing that Delphi is like a younger female clone of Tom, which may or may not be the point at which Harry realizes he's attracted to Delphi. (Meanwhile, Delphi also has some very confused feelings toward the diary's memory of Tom Riddle. She's pretty immediately smitten... until she realizes that he's not only obviously related to her, but also that he grew up to be the snakeface serial killer styling himself Lord Voldemort.)
During second year, Delphi rigs up a way to stay in contact with Harry (possibly inspired by her father's diary). [REDACTED]
While planning Hermione's schedule for third year, Minerva McGonagall applies to the Ministry for authorization to allow Hermione to use a Time Turner to take more classes than would otherwise be possible. When Snape catches wind of what is happening, he knows damn well that he won't be able to prevent it, and so he pressures Delphi into taking on more electives so he can further prop her up as the Slytherin rival to Hermione. Delphi acquiesces, filling her schedule with not only the requisite Astronomy, Charms, Defence Against the Dark Arts, Herbology, History of Magic, Potions, and Transfiguration, but also Arithmancy, Care of Magical Creatures, Divination, Muggle Studies, and Ancient Runes. (Note that while Rowling claims Hermione's time turner was the only one to ever come to Hogwarts, that's fucking impossible. The teachers must be using them or something similar, along with the overachieving students. Because he did Percy and Bill Weasley and quite possibly Barty Crouch, Jr. all get twelve O.W.L.S. when Hermione could only take ten classes without resorting to time travel??)
Dumbledore MUST tell Delphi about the blood protection this year; otherwise, she's going to go through with her promise to make sure Harry doesn't go back to the Dursleys. Lucius would probably actually help her in order to get Harry Potter away from the safehouse where he lives and into a much more breachable location (or, hell, his own home for ample brainwashing possibilities).