When opening a phone screen is too dangerous, the alert still has to fire. Silent mode keeps the screen dim and the device quiet so an aggressor remains unaware.
The job is to respond and disrupt — interrupt what is happening, witness it, keep her safe, and hold the scene until official authorities arrive. Responders have no powers of arrest and are not private security. Every responder sees these prompts on screen before they arrive, and agrees to them in writing through their organisation.