In a new interview (in French) Clemence, who played Fleur in Goblet of Fire, said:

For Harry Potter, I spent eight months in London. I was lucky, I am very grateful the producers chose me. They work with class, honesty and ethics. They only see how they leave their free and independent young performers. My participation was modest. I was flattered to find myself on the poster, given the scale of the phenomenon. If I was recognized on the street, it was thanks to Harry Potter. I have not read the last two books. I know that my character returns, but I have not been contacted for the sixth movie.

Hopefully, Clemence will be contacted soon about Fleur and will indeed be in Half-Blood Prince