Actually, no - under well-established case law and statutes, a call to 911 does not impose a liability on the police. They'll get there when and if they can, and if you die in the meantime, it's not their fault.
One of the only circumstances where this principle doesn't usually apply in most states is when someone is under police protection for a specific reason, such as being a material witness in a mafia prosecution.
Oops, I mis-spoke. The legal duty was established the moment the city agreed to send a patrol car to the location. “. . . [V]oluntary assumption of a duty to act carrie[s] with it the obligation to act with reasonable care.” Furthermore, it can likely be established that the victim
relied to her detriment that the police would promptly respond. In other words, her attorney will likely argue that, for example, the victim did not flee the area because she believed the police were on the way.
The seminal case (where the above quote and reasoning appear) in this regard is a 1982 case, DeLong v. Erie County., 89 A.D.2d 376, 455 N.Y.S.2d 887. It is taught to most first-year law students.
The city will settle out of court.