What is the turning point in Sadie's life in the novel, Whispers Through a Megaphone?

After drinking too much, Sadie and Alison decide to take a taxi home. When the taxi driver crashes his car, Sadie is in a state of shock, but she ultimately decides her future while stuck in the back of a wrecked car. This scene is brief but formative for Sadie. She realizes the critical aspect of this moment and how it serves as a turning point in her life. She hits the wall, both literally and figuratively, at the same moment. Sadie relays random details of her life with Ralph to a stranger who arrives at the scene to help, providing her with the tools and insights she needs in order to decide how to move forward with her life. Will she choose the life of suffocation, similar to the perfumed woman who tries to help her get out of the car? Or will she choose the confidence and independence Alison shows while catching the fleeing taxi driver?