I also don't think Prada would be something that would fit into Doutzen, but I think that of those bigger brands (that she doesn't have a campaign) is one of the few she has more chances considering the professionals who work with Prada. But anything can happen and if she is a good model she may be versatile enough to make a good campaign! Prada generally likes models a more different kind of beauty, but has a somewhat diverse background if we recall some models that had campaign for the brand, Miranda Kerr, Toni Garrn, Natasha Poly... I can see Doutzen in a campaign like S/S 2009. Despite the Prada problem these days I think it's the horrible clothes. So I think that if it were not to change the style of clothing to be something more appropriate to the type of work that Doutzen does, they would have to create a context for the campaign to be good, as Moschino does with excellence.
PS: I think Moschino is the worst brand in the world, but the campaigns are great because they create a perfect context for clothes! Like D&G used to do in 00's.