Doing ANYTHING solo will always be more dangerous and more expensive "per person" than doing it with a partner because of the simple math involved. However, by the time you have finished reading Vanabode you will see that you can safely travel alone, that you can cut costs, and regain your life's freedoms while single. You will also see that though you may go solo, you will not actually BE alone.
You will still be functioning in the world, still working, buying supplies, interacting in public places like national parks in Washington and clubs in Vegas, having fun, being out among people. You won't be lonely that is for sure.
Most peoples concerns about safety while travel camping in a Vanabode stem from one simple illusion that everybody seems to have: That is: most people think they are safer in their house than they are in a Vanabode traveling around. This is NOT true and I prove that in the Safety, Weapons, Security chapter in the book. Overall the Vanabode lifestyle is safer than holing up in one house for your entire life.
I think however, that your question is more about how safe the lifestyle is as a single person, rather than is it safe at all? Well lets break it down. What are some of the tasks you will complete alone, that you would have to do differently than say my wife does? There are not that many really.
1) When we are visiting a museum and she goes to the bathroom....well I don't go with her. So there is no difference there.
2) When she goes to the bathroom out in the woods on a long hike, I am nearby, but since I have NEVER had to defend her once against another person, animal or insect, I have to assume that she was never in danger to begin with. In otherwords you would be just as safe as she was with me there, even though you may find yourself in that position alone.
3) If you are working one of the seasonal jobs from the companies listed in the book, or at a national park, or even in a set location, there is no difference.
4) As a single person I would make the following changes to my lifestyle so as to employ the greatest advantages possible. I would purchase a AAA membership or similar from your insurance company so that any mechanical breakdowns are covered by professionals. I would not camp near groups of adult males that do not seem clean, polite and harmless. I would work in the larger of the companies rather than the smaller more remote ones if I were to take employment rather than working from the van on the Internet. I would not drink unless I had a hotel room to stay at for one night. I would not advertise that I was travel camping alone. I would check in with someone on a scheduled basis, say "Mary gets an email once per week from me, John gets a Facebook update once a week from me, and Sue gets a phone call every 4 days just to check in and say I am fine." Then if any of these parties do not get the scheduled contact they are instructed to "find you" via whatever method you have set up.
My final point is this. Vanabode travel done as I describe in the book, is no more dangerous than living in one set location. Therefore Vanabode travel is no more dangerous for a single lady than living in one set location would be for a single lady. The things you look out for, and the issues you cover to keep yourself safe, are the same.