First off, it’s not SAFE to do much of anything. It’s dangerous to fly, more dangerous to drive, and dangerous to send your kids to school. Even having kids is dangerous (the the mother). Nothing is SAFE. I believe it is SAFE ENOUGH to let an 11 year old kid fly alone. Air travel is very safe, both in terms to transportation accidents, and the danger of abduction or assault, because there are lots of people around whose job it is to keep it safe (including flight attendants). To the extent that this story is accurate, it is highly unusual, which is why it make the news. For every child or woman this has happened to, hundreds have flown safely. All of this can be reduced to a game of odds, risk, and severity of injury.
There are things people can do to reduce their chance of harm. If you wear a seat belt on a plan, you greatly reduce your risk of in flight injury. If you yell when a stranger touches you in appropriately on a plane, you greatly reduce the risk you will be sexually assaulted.
I’m in no way blaming the victim, but when I was a kid, I was told to yell for help and run away if I was in danger. There must have been at least three or more flight attendants on that plan, and plenty of passengers who would have come to this girls rescue if she yelled for help.