The idea is to get out ahead of all the social networking bits, and create a deliberately blank slate. All of that stuff is placeholder, neutral, for as long as the kid wants it to be so. The kid's free to fill all that in, or not, but the child won't start with a bunch of their personal data filled in. That last part is consistent with the stated beliefs/goals of the author, bearing in mind that over time data only accretes and there's no undo.
'Desirable' usernames are, technically speaking, as close to irrelevant to privacy as you can get. Your behavior with an account is what matters for privacy, not the account name. [1]
Yet the article is entirely about the account names and only somewhat in passing about the sorts of lessons the author hopes her daughter learns about "how (not) to conduct yourself online".
And without those lessons... you can 'protect' facebook.com/janeannsmith all you want, but if your daughter makes privacy-eroding mistakes with reddit.com/u/sparklepony2031 -- those can be trivially connected to facebook.com/janeannsmith the second you hand over the 'keys' to that account.
That's the whole point about the loss of privacy online. Once the accounts are associated to you, those associations last forever and follow you immediately and irrevocably anywhere else an account becomes associated to you.
[1] sure, sure -- using your real name as a username is Bad For Privacy, but the author wasn't talking about janeannsmith vs sparklepony2031. They were talking about janeannsmith vs jane-ann-smith and janeannsmith vs janineannsmith -- should jane ann smith have turned out to be the name of a porn star or third world dictator or some such.
Frankly, as far as privacy goes via name conflicts, you're better off being named Mike Johnson and having lots of collisions, even if some are negative, than having some unique name that doesn't have an online association yet. Some plausible deniability is better than none.
However, for branding, the opposite is true. Which, again, underscores how the author's behavior seems to be much more about branding than privacy.
The idea is to get out ahead of all the social networking bits, and create a deliberately blank slate. All of that stuff is placeholder, neutral, for as long as the kid wants it to be so. The kid's free to fill all that in, or not, but the child won't start with a bunch of their personal data filled in. That last part is consistent with the stated beliefs/goals of the author, bearing in mind that over time data only accretes and there's no undo.