She followed the river downstream until she found a shack, because her father had once told her "If you follow the river downstream far enough, it will always lead to civilization." So yes, she did have plenty of drinking water available, if nothing else.

There's no question that she was extremely lucky, in many ways; but like many survivors, she made the most of it when it came her way. The others had the same luck, if not better; and they squandered it.