Honestly the real threat isn't a mugger or somebody hiding in the shadows at night. It's some guy spiking her drink at a party. It's the guys she's around when she drinks to much. The real danger comes when she couldn't defend herself even if she had a gun. It's tough to come to terms with, but the best thing you can do for her safety is talk to her. Don't let your drink leave your sight even for a second, have someone in the friend group take it easy and look out for everyone, and pace yourself.