I understand your concern but it isn't only limited to females who are "alone". The whole world is nuts. You have cops getting attacked in NYC, people getting shot at Super Bowl celebrations, people getting shot in church, and we all know about violence in our schools.
There is no universal "magic pill" to curb this. We simply live in a violent society. Yes, it's awful and I certainly don't have the answers. There is nothing wrong with being cautious and being aware of your surroundings. I get that. But if I want to do something or go somewhere, I do.