Has she gone to school yet? A qualifed trainer could help you out as well. The more exposure you can give her to different situations, the better. The more handling by all sorts of people, the better. The more animals, the better, the more noises, the better!! All of this will help her learn to be calmer and more dependable in all situations.
I have found female Newfs to be a lot stronger in temperment than the males. Mine was more protective, stronger willed and her nickname was "Little B*tch"!! for a very good reason.
She is SOOO adorable, though!!