I bet when the DVD comes out, the behind the scenes extra will feature a whole segment with the animators discussing the challenges of creating her hair. Should be fun to watch. I think the choice for curly hair might reflect the change in how curly hair is being perceived, but also the fact that 3D animators are always looking for the next big challenge as far as creating textures goes.
I don't think - and I hope I'm right - they will straighten her hair in the end. It's too beautiful for anyone to want to mess with it. And why go through all the trouble of creating those curls if they thought straight hair was better?