Even if this little girl knew how to swim, statistics show that unless she is a competent swimmer her chances of drowning are even higher.
Those who have fair swimming skills get over confident and will enter water where they're not suppose to.
You're taking the marginal cases and making it as general. Can an advanced swimmer drown? Of course and as you say, this is usually because they overestimated how far and how long they could swim. But this is marginal and extreme. Under no circumstances would it ever be reasonable to say someone has too much swimming skill. Would you ever say a person has too much firearm knowledge and skill? No, it's not reasonable because most accidental discharge usually involves younger people who are curious and have no knowledge about firearms.
If you haven't heard, there was another Lake Elmo drowning just a week ago, this time a 27 year old Hmong man:
http://www.twincities.com/2017/06/16/lake-elmo-drowning-victim-identified-as-woodbury-man/(I didn't want to post a new topic because I'm getting sick and tired of these preventable drownings)
If that Fresno and this Lake Elmo Hmong man knew just how to front stroke 10 yards and were comfortable enough in the water to not panic just because their feet can't touch the bottom, I think their chances of survival would've been greatly increased. Had the six year old girl knew how to do a pitiful doggy paddle, I think she wouldn't have drowned. In all three of these recent cases of Hmong drownings, ALL THREE OF THEM HAD ZERO SWIMMING SKILLS. I can't recall ever hearing of a recent Hmong drowning that happened even though they knew how to swim. It's always because of a lack of swimming skill.