Lynn Collins does not look like Dejah Thoris to me, but put some red make up and remove her clothing and she might look more the part. Traci Lords’s face is not oval and her hair not black, so she doesn’t look like Dejah Thoris at all.
My daughter, who is now six, could handle the vocabulary of these books. Sure there would be a few words that she might need to ask us, but I am betting not all that many. People do have a tendency to dumb things down for children nowadays. I do think some of her friends would balk at the big words, in part because their parents laugh at people who have large vocabularies.
I read an article once by an author who wrote for children’s shows about a list of words that he had been given to avoid because they were too hard for young children. Among the words on the list was "furnace, which I found absurd because my daughter understood that word when she was two. We never dumbed our vocabulary down for her.