I agree Wendy in the movie was not done well at all. And she is supposed to be blond.
I did not like Wendy or Jack much. I was pleasantly surprised to find the characters of Doctor Sleep to be extremely likeable. I find that, in his early works, Uncle Steve did not create really strong women characters. I find Susan and Frannie to be almost the same character. Now his work is more mature and his women are as real as roses.