Thanks for the file.
In a slightly older post, I link to an interesting cite where you can check out a human voice "radio style" broadcast that splits up frequencies really well.
I find that the 1 khz region is perhaps critical for sibilance, but also where voices actually start to become intelligible. It was definately around 4 khz - 10- kHz on up where the "sizzle" starts to show up - but at that point, you could not know what was being said or sung. Hence, it would seem that, at that point, while their may be some voice wandering into those frequencies,the female's voice is less important than the overlap with whatever instruments. Supposedly, you might boost those higher freqs for the sake of putting some "air" around her voice.
Its interesting because the tizz sounds almost like a slight distortion - either in the recording, or in the phones. To my ears, it is somewhat like static. I have played around with severely rolling off freqs from 4-20 kHz and dropping 1 kHz, but it doesn't make much difference other than dulling the listening experience. So I am chalking it up mainly to "revealing" phones and "hot" recording. Not all female vocals create this issue, though now that I am noticing it, I am noticing it everywhere! My HD595s even seem to reveal a similar issue. I guess each new pair of headphones trains my ears a little differently.