Since this article is still on the front page I would like to ask HN how does one deal with the similar issue of letting a young girl know she's pretty without suggesting it's of central importance
Well, my approach would be not to bother letting her know she's pretty. Let's face it, unless she is unlucky enough to be "ugly" in a way that removes her from the accepted norm, there is a high probability that somebody somewhere will date her and love her when she is older.
Not to discount the effect that our culture places on girls and physical attractiveness, but girls learn much from their parents, especially there fathers. If she can see that what she looks like doesn't matter to you one iota, odds are she will not see any real value in any guy that mentions how pretty she is. You can't be swept off your feet by somebody calling you pretty when being pretty isn't how you define your worth.
In other words, by worrying about her getting the pretty comment from you, you're probably working against your intended objective.