During the first wizarding war, Voldemort made a choice. A choice to spurn his followers notion of purity, to step beyond his country and sway others to his cause. Other groups, other races.
One of those were the Veela.
And thus the war raged on, more devastating than could ever have been thought. Terror and death was wrought by Voldemort's forces, bolstered by their new allies, by the fire and allure of the Veela, the sinister rituals of what remained of Grindelwald's supporters, and so many more.
Yet, it all came to an end, one fateful day, when a little boy did the impossible, and vanquished Voldemort in a cottage in Godric's Hollow.
This was the world Fleur grew up in. A world where her family, her kind were forced to hide amidst muggles, suppress their very beings to blend in, in fear of a wizarding community that felt justified in their hatred of all those who had stood with Voldemort, the Veela not the least among them.
Yet, Fleur was a rebellious child. She hated the hiding, the constant need to look over her shoulder, the need to deny who she was. She hated muggle Britain, where her family hid, with its constant cold and its drab atmosphere. But most of all, she hated Harry Potter, the boy who, in her mind, had caused this. Without him, the Veela would have been free, free from all that had plagued them before the war. Free from the lust, the discrimination, the objectification, that her aunts always talked of.
Yes, Fleur hated Harry Potter with all her heart.
That was, until she met a little boy, working in his relatives garden in the rain. A little boy, with kind green eyes, a nervous smile and a lightning scar on his forehead.
TLDR: The Veela join Voldemort in the first war, and everything changes.