I'm female and I walked solo from Ponferrada to Santiago last fall. I felt extremely safe and minded my own business. I carried a whistle, but never needed it. My hiking poles served as a deterrent once when a dog approached me a little to fast. On my day to Palas de Rei an oldish man stopped his car next to me and asked if I wanted a lift, I graciously but firmly refused. Basic personal safety rules apply wherever you go, same holds for the Camino. Watch for speeding cars in blind turns when you are walking on the road. If you plan on walking before sunrise, wear a reflective vest and other reflective paraphenalia over and above using a headlamp or flashlight. Common sense should prevail. If you don't feel comfortable in a situation, quietly leave the situation and seek to be among other pilgrims. Avoid getting drunk beyond your faculties (anyhow the hangover would prevent you from walking the next day). I think that should cover it. The only guns you can have are your biceps; the only mace, used for cooking; the only knives, for slicing tomatoes or cheese.