Jodi Picoult's novel are known for innovative twists and unusual deliveries. Nineteen Minutes is no exception. The issue here is the bouncing back and forth from past to present. This accomplishes a couple of things.
The first thing this accomplishes is it keeps the reader on his or her toes. Sometimes, spending the entire story in the present tense, readers have a tendency to become complacent in the reading of the novel. We know what to expect, and our attention can relax. Jumping back and forth, keeps the reader's mind involved.
The second thing this does is establishes a means of successfully fulfilling her goal with the novel. From very early on in the novel, we know the fatalistic outcome. We also know that the protagonist's daughter is going to be swept up in this fatalistic outcome. Switching back and forth creates a more sympathetic audience for the conclusion as we can almost understand the progression of the tragedy.