Hmm...have a quick google around and see all the different pictures of Ciri. There are very slender, tall ones, shorter ones, boyish ones, more elegant styles...etc. The only thing that seems to be in common is her long,straight, ashen hair (though i have seen a couple with wavy hair). Other than that, she differs a fair bit. So unless there's a picture that the author himself drew, someone's appearance based on a description is kinda like making a cake based on saying what it looks like rather than having an actual recipe. This is like the Yennefer thread. I find both threads a little nit-picky-ish.
Though i do agree there are some specifics that CD should stick to, and everyone agrees on, a person's appearance based on description is rather a subjective thing.
Even moreso with races that don't actually exist, such as Elves. To me, i think LOTR. And they were all tall, slender beings in those movies. So if Ciri is meant to be of Elven blood, that's how i imagine her.
One thing though, someone mentioned she's meant to be 20yo? She looks a fair bit older in the trailer to me. I get it that she's been through a lot, but her age doesn't quite match her face.
As far as her hair goes, she seems to have it tied back and up in the trailer, so maybe there will be scenes in which she has it out.
As she is now, i like her. But i'd be more worried about her character and getting that right, rather than how long her hair is, or what shade of blonde. Much like the Yennefer thread. I'd rather CD get both their characters right.