Perhaps a plot twist where Fem Harry discovers that the Goblet of Fire was actually tampered with not just by the obvious culprit, but also by someone she trusted deeply. This betrayal would add a whole new layer of drama and mystery to the fanfiction. She would then have to deal with the fallout while still competing in the dangerous tournament.
One interesting plot twist could be that Fem Harry forms an unexpected alliance with a Slytherin student. Maybe she realizes that not all Slytherins are as bad as they seem in the context of the Triwizard Tournament. This changes the whole dynamic of the story as she now has an inside source in a house that was previously seen as her rival.
A really cool plot twist could be that Fem Harry has some latent magical ability that is awakened during the Goblet of Fire events. For example, she might discover she can communicate with magical creatures in a way no one else can. This would give her an edge in the tasks of the tournament and also change how others view her, from just being 'the girl who survived' to someone with extraordinary and unique powers.
One interesting plot twist could be that Harry has an unexpected ally in the Triwizard Tournament. Maybe a Slytherin student who has a hidden agenda but ends up helping Harry in a crucial task. This would change the dynamic of the traditional House rivalries.
One interesting plot twist could be that instead of Cedric Diggory being the Hogwarts champion, Neville Longbottom is chosen by the Goblet of Fire. This would completely change Neville's character arc in this part of the story, as he'd have to face much more danger and scrutiny. It could also lead to new friendships and rivalries.
One interesting plot twist could be a character who was thought to be a friend actually being in league with the Death Eaters all along. For example, a minor character like Seamus Finnigan could be secretly working for Voldemort, passing information about Harry's movements. This would add a whole new layer of danger and suspicion to the story.
A great plot twist could be that the Goblet of Fire was actually tampered with by a group of former Death Eaters who wanted to bring back Voldemort in a different way. They planned to use the tournament as a cover to perform a dark ritual, and Harry uncovers this plot halfway through the story.
A possible plot twist is that Draco is secretly helping Harry in the Goblet of Fire tasks. He might do this because he realizes that there are darker forces at play that could harm not just Harry, but also Hogwarts and his own family. So, he uses his knowledge of the dark arts in a positive way to assist Harry without anyone knowing.
One interesting plot twist could be that a different student is chosen by the Goblet of Fire instead of Harry. Maybe a Slytherin student who then has to deal with the suspicion of being in cahoots with Voldemort. Another could be that the tasks in the Triwizard Tournament are completely different, like instead of facing a dragon, they have to solve a complex magical riddle within a dangerous enchanted forest.
One interesting plot twist could be Snape secretly protecting Harry throughout the Triwizard Tournament in a more obvious way in the fanfiction. Maybe he uses his potions skills to give Harry an edge without Harry realizing it's Snape helping him.
One interesting plot twist could be a different champion being secretly controlled by Voldemort instead of just Barty Crouch Jr. as the imposter Moody. Maybe a champion from a different school who no one suspects.
One interesting plot twist could be that Hermione is secretly entered into the Triwizard Tournament not by the Goblet, but by a dark wizard who wants to use her as a pawn. This would put her in a very dangerous situation right from the start.
One interesting plot twist could be Draco secretly helping Harry Potter in the Triwizard Tournament tasks. Maybe he realizes that there's a greater danger at play that could affect both the wizarding world and his own family, so he decides to put aside their rivalry for a while.