I would tell my daughter--and son--to bring someone along with them, generally. However, I hiked alone for years; indeed, I completed almost a thousand miles of the PCT and often hiked alone. I remember crossing the snow-melt, raging,Kern River alone; glissading down Whitney Pass on a poncho over the snow which covered the switchbacks into Muir Wilderness ; being shot at whilst taking a "small" shortcut through an Indian reservation. Looking back I think I lucked out quite a bit, for all it would've taken was one slip up. I cut myself up pretty good on the rocks gliding down Mount Whitney, too. Wow. So why not bring a friend if at all possible? It's funner, too, generally to have someone to bounce thoughts off of, etc. And I have had a few run-ins with foul mannered folk over the years, all near trailheads (now that I think about it), and though the instances have been very few, I'm still thinking that I'm over twice the size of my daughter (wrestled at 285) and some folks still feel the need to cause trouble (or are feeling alcohol) so why not bring a friend along?