The people being killed in Mexico, by and large, are not foreign travelers, they are Mexicans who are involved in drugs. Looking at the average murder rate is misleading in this context.

It's not particularly wise for a young woman to hitchhike in the US either. I certainly wouldn't recommend someone do it right now in Mexico, and I have no doubt that people here and there all have fears about it, but fears don't necessarily mean it's extraordinarily unsafe.