Honestly, it is SO difficult to sex any of my current silkies because they all had vaulted skulls and have nice round crests. I'm REALLY watching for streamers at this age. Of course, I'm watching behaviour and comb sizes as well.
-As for Powder Puff....I go back and forth thinking s/hes a pullet and then cockerel! The behaviour is neither shy nor aggressive. And, even the stance varies from walking low (like a girl) to strutting and occasionally chest bumping. With PP I can't even use the single comb as an indicator.
But.....If I had to guess, I would say Powder Puff is a girl. I hope yours is too.