BINGO! I could not have said it better myself. This is the whole problem with the second film.There was nothing in the first movie to suggest that the specific duties of being Queen was Elsa's concern. It was about the fear of her not being able to control her powers and potentially hurting people like her sister again.
The movie ended with the gates open and Elsa using her powers in front of people and they were fine with that. Outside forces posing a threat to the Kingdom makes sense for a new conflict/story, but changing the outcome of the first movie does not sound like good storytelling to me.