Mrs. Hardwicke claims in the commentary on the twilight video that she had other engagements that prevented her from working on new moon.
I got the distinct impression when listening to her though that she was not interested in the project.
Stina in a way I agree with you. There was much Mrs. Hardwicke left out of the movie that really should have been in the movie. Things which are in the books, which make the storyline make more sense.
I felt that in a way Mrs. Hardwicke dumbed the movie down some. Of course I'm not a huge fan of her other work either anyways.