Based on what I've read, nobody who has posted so far has a clear understanding what singlehanded sailing is all about based on the lack of discussion in that direction. This is an incredibly dangerous endeavor. One shipping container that has fallen overboard from a freighter, tree trunk, or even a pod of curious whales can cause your untimely death, never mind being run over by a commercial ship, or making a navigational error and striking land while you are asleep or preparing your dinner. It happens all the time.
Then there is the issue of rogue waves and weather. While planning your trip to avoid hurricane and monsoon seasons goes a long way towards eliminating the danger, there will always be times when you are at risk of being capsized. The odds of this occurring are inversely proportional to you actual sailing experience under those conditions and the seaworthiness of your vessel. While the latter will likely be exceptional in this particular case, there are always issues of equipment failing and what you can do about it while on the high seas.
And if you ever fall overboard, forget about it. The odds of you surviving are close to zero even if you are attached by a harness to a jackline. Most people simply don't have the strength to be able to pull themselves back aboard. Every time you leave the cockpit, you are risking your life.
Then there are the psychological aspects. Being completely alone for days on end with no human contact whatsoever while surrounded by thousands of miles of open water is sufficient to drive many people nuts. It would take an incredibly mature and independent 14-year-olf girl to really want to be that isolated from civilization for such long periods of time.
If you really want to know what singlehanded sailing actually entails, and why it is completely different than sailing with sufficient crew to stand watches or help in times of emergencies, I suggest you read this most excellent book on the subject:
Singlehanded Sailing: The Experiences and Techniques of the Lone Voyagers
And a 14-year-old girl will face a completely different set of problems from your typical amateur sailor. She is obviously going to draw a lot of attention wherever she sails. Unless her parents are rich beyond belief or she has a support organization that will always watch over her when she is in port, that could very well be the most dangerous aspect of her trip.
And someone mentioned Lloyd's. No insurer will cover a singlehanded sailboat under any conditions. You must always have sufficient crew to stand watches while underway to even be considered for insurance for obvious reasons.
That route is completely impractical for the typical sailboat due to lack of provisioning ports and the incredibly high seas you would face. Amateur sailors go out of their way to almost always pick the route where time between ports is minimized as much as possible, especially if you are singlehanding and only taking catnaps while you are underway.