We won't know for sure until late October or early November when she finishes moulting. If after the moult, she still has yellow on white bars under her tail, she's a girl. If her tail feathers are solid, then she's actually a boy. Cockatiels are all born looking like little girls, with the yellow bars under their tails and the same colouring.
She hasn't been dropping many feathers lately, so she might be done. But it slowed down a bit earlier this summer and then started up again. So far, she still has two tail feathers on either side with yellow bars.
Skippy's quite vibrantly coloured (boy sign), but Lutino females sometimes are. She's a little too chatty to be a girl. Hens usually don't vocalize much at all.
She's also doing something that sounds like a wolf whistle which is very much a boy sign. It sounds so wrong it's hilarious, but we think that's what she's trying to do. She does two flat pitched squawks. The first note is consistently higher than the second note and there's an awkward half break in between. So we know she's doing it on purpose. =)
But she's starting to learn to do the pitch variance that we do and closing the gap between the two pieces so that it sounds more like a wolf whistle.
Sid's wolf whistling and flirting isn't working on her. The only girl in the house that it's working on, is me. =)
The only way to find out 100% for certain is a DNA test. A breeder might need to do this, but we don't need to know badly enough to pay for that. But, for now, I'll have fun saying that Skippy is either a Tomboy or a Metrosexual.