The Supreme Court and upheld more than once. The police have no duty to intervene or protect you from a crime. They are there to enforce the law after it is broken.
People want to think of the police as super heroes that will save you, and therefore think they can defer their responsibility of their own defense to a bunch uniformed strangers, because they don’t want to confront the reality that it is their own responsibility. Burying your head in the sand leads to dangerous policies as well as vulnerability by being wholly reliant on someone else in this regard.
I do feel badly about this case. Given that the police failed to act on the complaints, she probably also would have been punished in some way and run afoul of law or policy in some way for taking her own protection into her own hands. She was in a lose-lose situation. From that standpoint, I can see things from the parents’ perspective.