Florian Gallenberger was interviewed about Colonia & Emma Watson at the Edinburgh International Film Festival.
Here's the part in which he talks about Emma.
Emma Watson’s performance was a particular highlight. Did you always have her in mind for the part?
In the beginning, we planned to do this as a German film. with German actors and German language, and then it turned out that the size of the film that the financing we couldn’t raise from Germany alone. Then we realised that there is a dimension to the story that’s bigger than just Germany, so we decided to shoot the film in English. Emma was top of the list, as there were two things that were important for this part. The first is someone who you believe has a strong inner conviction; a strong person inside, but still a fragile person on the outside. I wanted a female hero who has a different type of strength, and that’s totally Emma Watson. She’s so convinced about the things that she’s fighting for, and she’s a very fragile, beautiful woman. The Colonia, to me, has always been a place of darkness, and I always wanted someone who radiates a certain brightness. That’s like magic, that’s what Emma does; if she’s in the frame, you just look there. She has the quality of a lamp. So I wanted to bring this bright, fragile character with a lot of inner conviction into this world of darkness to face this system. We had a casting agent here in London who was very helpful, then we got the script to her and she liked the material.