Didn't say she was. I've been on the sea and in the sea many times in my life. In my universe, anyone who goes SCUBA diving or sailing into the deep sea alone, needs their head examined.
Well..., in that case, you're going to be taking issue with quite a number of people who encourage and/or support endeavors like that. This is not, by any means, the first time and nor will it be the last time.
If anyone could make a legitimate argument out of that kind of rationale or reasoning -- then many others would be in mental institutions right now and/or parents would be accused of "child abuse". But, since you can see that they aren't (in the mental institutions and/or being accused of child abuse) -- it's obvious that this argument doesn't carry any weight in society, but is seen as a matter of a legitimate choice and decision.
This is a 16 year old child off on a self-indulgent quest. ...in 60 knot winds with 50 to 60 foot waves. Now others have to brave that weather to find her. This isn't some noble cause she's taken up. She just wants to state that she sailed around the world at 16, alone. If she lives. At 16 she doesn't know what LIVING is let alone dying.
This sailing trip aside....
You know people who go SCUBA diving alone? Not anyone rational or PADI certified I'll wager.