The prophecy really didn't help much either, in my opinion.All it did was kind of foreshadow to the problems there would be later in the movie, which was Elsa's powers.
And didn't the king say that she was born with them, not that they appeared over time?
It also seemed that the first time Elsa's father and the troll king talked bout her powers was that first scene in the movie.
It just seemed that way to me because of the questions the troll king asked and how he had to explain it.
Plus the king died before he could have even attempted to deal with Elsa's powers, assuming that he was prepared.
Not that it would have mattered if he was alive during the whole movie, it still would have been Elsa and Anna to save the day.