I don't have time for your breakthroughs! I have to save Nolan.
You can't leave now. We had a breakthrough.
After finding out that Helena has Nolan, Sunshine calls Ashley to pick her up from Llevar La Luz to drive Sunshine to Ridgemont. Sunshine runs out of Aidan's lab when Ashley honks the car horn signaling her arrival.
Aidan and Lucio try to stop Sunshine from leaving because there has been a a new break through in Aidan's research with Sunshine that will change everything. However, they can not stop her in time.
This scene is significant because later in the novel when Sunshine finds Nolan and Helena, Aidan tells Helena about Sunshine's progress: how Sunshine was able to help dozens of spirits move on by herself. This is important because it helps Sunshine realize that she actually helped Aidan and the world. Without her leaving, this would not have happened.