Dennings did have an arc! She realized that she loved her intern during a climatic moment.
But gotta love her character because these kind of movies NEVER have a character like Darcy. If they have a comic relief character, it is usually male. I think she was an extremely lively and unusual addition to the movie.
I frankly want even more of her next time. If I were the writer of Thor 3, I would make her one of the co-leads. I think she is a priceless character.