I haven't seen the movie either. He directed Mona Lisa smile... unfortunately, I haven't seen that too (time contraints on my end). Here are infos I got from imdb: http://www.imdb.com/name/nm0001565/
One word: Cosmetics 😉
They can totally make her look different in the movie with make up and it doesn't even have to be noticebly on her face to change or enhance the general look of it. It's also a similar case with Fleur where hair colour and make up will probably play a big part in getting the right look. The important thing is that they can act, looks come second because as seen in the music and movie industry make up can make anyone look stunning.