I've never watched the Tudors, but a quick google of the actress's name shows that she does not look sweet and certainly not innocent.

I'm more than willing to forgive that though, and the age, as frankly it doesn't matter all that much. Nearly 30 year old actors and actresses have played teenagers in the past and done perfectly well, so that makes no difference to me whatsoever. I am pretty concerned about her having more screen time than she is supposed to in the book. And something tells me that she won't be keeping her clothes intact all of that time either. But anyway, we'll see I suppose. I will remain pessimistic as ever though.