The author has stated that Daphne’s canon sister Astoria doesn’t exist in this version of events because it was felt there was more potential in Daphne as an only child and because it’s easier writing about her family without having to take Astoria into account. However, there is an additional implication to Astoria’s absence; since Daphne grew up alone, she may have been more interested in making friends at Hogwarts which prompted her to approach Harry, whereas in canon she decided that her sister was enough for her and her fears about her family reputation led to her not taking the ‘risk’.
It’s never explicitly stated, but certain parties (Snape in particular) likely see Harry and Daphne’s friendship as a gender-inverted version of Snape and Lilly’s friendship when they were at school. Snape even has a slightly wistful expression after a confrontation with Daphne in Chapter 37 where she complains about his attitude in a manner that would not sound out of place coming from what we know about Lily.
Snape confirms the observed similarities in a talk with Daphne in Chapter 60.
Despite her canon distaste for Divination, Hermione shows a surprising amount of faith in Daphne's visions. However, Hermione's problem with Divination in canon can be summed up as her disapproval of Professor Trelawney's teaching methods; by contrast, Daphne has genuine talent in Divination that allows Hermione to see clear results, even if Daphne doesn't like what she sees.
Some reviewers have criticised how Daphne can anticipate certain details but events still happen as in canon; most notably, she and some of her Slytherin friends guess how someone could enter Harry into the Triwizard Tournament against his will but it still takes place regardless. However, the actual success of the plan is justified in-narrative, as they would have no way to know when someone put Harry's name in the Goblet (and certainly wouldn't know that Barty Crouch Junior was a suspect to watch out for on the Map even if they could stay awake all night to watch it that way). As for Daphne guessing the plan in advance, this is an extension of her Slytherin upbringing; in keeping with Daphne's loose status as the Token Evil Teammate, she's simply naturally used to thinking a certain way that her more straightforward Gryffindor friends aren't.
Fridge Horror
Ginny is taken down to the Chamber after Hermione’s attack and survives there for a few days before Harry and Daphne come to save her, whereas in canon a few months elapsed between Hermione’s attack and the final confrontation. It’s not hard to speculate that Riddle in canon used those extra few months to gradually exert more influence over Ginny to ‘prepare’ her for the moment when he would use her to gain a new corporeal form. However, that raises all kinds of disturbing possibilities about what Riddle forced Ginny to do during those few days alone in the Chamber to increase his influence on her when Daphne’s words inspired Ginny to actively reject him…
