Luckily, the criminals were no longer on the place. Had they been, she might be dead--the loud noise would have revealed her location and the fact she was making a 911 call to the police. She had no idea her phone would do that--she had not been warned.
Many people have used their cellphones to place emergency calls in situations (carjackings, bank and other business robberies, home invasions, etc) where it was important that the criminals not realize a call was being made. Thanks to such calls, lives have been saved, crimes-in-progress have been stopped, and criminals have been caught.
A loud noise from the phone, revealing the call and its type, negates these possibilities. The noise reveals both the location of the caller and the nature of the call--and criminals could quickly kill the caller before she or he could transmit information about the crime in progress.
A new FCC regulation requires cellphones to signal the caller when a 911 call is made, but that signal can be visual or auditory.
Verizon has chosen to make all its phones give a loud audible signal; users have no choice, cannot turn the signal off or choose a visual signal instead. That endangers anyone in the Verizon network who needs to make a call in a dangerous situation...especially those who do not know that their phone will make the noise, who are trying to make a surreptitious call and find that they're now "outed" to the criminals. Verizon needs to change its policy. All cellphone users should be able to make a quiet call in an emergency.