Predator or Prey

A woman exits a parking garage to her car and is accosted by a group of thugs. An odd woman comes through the same corridor, sees what is going on, and immediately tells the boys to leave. They don't and decide she is the next victim. She might be small and chubby, but she has a few tricks up her sleeve.
The woman is aghast and thankful at her help and questions her self for not doing the same. The woman tells her a truth that will change her life forever.