Five (5) different cases decided by SCOTUS say the police have no duty to protect any specific individual. At least one of those cases says the police have no duty to respond to a 9-1-1 call.
Are you suggesting that if the police did a better job when they showed up the lady would not have been killed? If so, please explain how/why.
It's a sad situation, but instead of piling blame on law enforcement we should be seeking ways to use this to educate the public about the fact that they are in fact on their own and that calling 9-1-1 will not save them.