What do you think is the most important thing that PJ should do well in RotK?

I would exchange her for the scourging anytime. Why does PJ places Arwen in the story so much. The only thing she does in the book is talk to Aragorn. She is being made some kind of superhero, while she did very little. I don't understand that. They could have made the battle at helm's deep bigger if they left out that stupid dream.