Part 1
During the TWT, there are many expectations of the champions, and Fleur is affected badly because she's the French competitor in Britain and because she is seen by some as not even human. She is coping, but it is not an enjoyable experience.
One day (after the second task), she runs into one of the Aurors providing "security". Keep an eye on the foreigners would probably be closer to what Fleur experienced so far. And she's quite surprised since that Auror had pink hair. They start talking, Fleur using the hair as icebreaker ("I didn't think that this colour is within regulations"), which prompts Tonks to talk about her experience in Auror training so far and that the security assignment is just something the Auror department has to do due to contractual obligations when Crouch and Dumbledore made Hogwarts the location. No one in the Auror department wants those tasks, so the trainees get the shitty assignments. Which is why she did not pay attention to her hair colour at all.
Fleur and Tonks start talking and Fleur admits that she'd love to dress/look more like Tonks, but she does not dare to because almost everyone has already been shitting on her without her doing anything provocative.
They talk some more until Tonks replacement shows up. The next time they meet, Tonks has come up with an "ingenious" plan. Fleur can have a makeover and if she does not like it, easy to unmake it with magic. So they start relatively harmless, a bit hair dye, but then Fleur makes more and more suggestions. It takes them a few hours to find out exactly what Fleur wants, but in the end, she really likes the new look. What exactly that is is up to the author, but given the inspiration I'd go for something similar to Harley Quinn, perhaps with a bit more punk influences due to Tonks.
Part 2
So Fleur spends the whole next day looking like that, chilling with her friend(s) and generally having a good time before Maxime shows up and reads her the riot act. Unbecoming conduct and whatnot. So reluctantly, Fleur undoes her makeover, but the resentment lingers. Fleur and Tonks start exchanging letters.
Maxime continues to be a bitch and eventually Fleur snaps, showing up to the 3rd task reveal with her new look, the "scandal" is fueled and used by the Ministry to cover up the disappearance and death of Crouch Sr.
Maxime is livid, but Fleur does not give a fuck. She's the champion, she's about to leave schools anyway, what's Maxime about to do, lock her up with bread and water?
A few days later, Harry tracks her down and they have a chat. Harry admits that he too would like to poke the hornet's nest like she did, but he isn't feeling a makeover and can't think of any other way.
Either write a romance from there on or make it Fleur/Tonks. If you go with Harry/Fleur, you could completely derail the graveyard if the two meet in the maze and decide to team up. Viktor ambushes Fleur, Harry plays human shield and is out. Either Fleur takes out Viktor and Cedric takes the cup in the meantime or Viktor is last man standing but under orders not to win, so whoever retrieves the trophy triggers the portkey (Fudge would be perfect for that).