Have you ever tried it or are you just imagining what it would be like? I've never tried myself it but I do know how well people adapt to things like this. You say it hinders her performance but how do you know? Maybe it would hinder your performance because you aren't used to it but that's a different matter altogether. Keypeg's point about shortening tendons aside, I don't see any evidence, or hear any real argument against wearing heels at the piano. She plays brilliantly in heels, as you yourself have said, but if you can show me her playing consistently better in flats then I will happily concede my point. Otherwise I feel like you're just guessing that they hinder her performance.
I wasn not seeking to compare her performance with and without stilettos, especially since I've hear far more of her on recordings and broadasts than I have seen her perform live. I cannot vouch for the extent to which anyone might find themselves having to adapt to pedalling while wearing such shoes but am attempting to apply logic to this in terms of the height above floor level of the tops of the pedals.
That said, whilst I had indeed never tried it, I did just now by placing my ordinary heeled shoes on top of a book around 3cm high and found that this impeded my pedalling ability to the point where I could hardly do it at all (OK, I'm not a pianist) and I cannot imagine that continuing to do this would enable me to become accustomed to it (and why bother ayway?).
Keypeg's point is also a very valid one that applies to everyone wearing such things often and long enough, not just pianists!
A little over 6cm is the height of the pedals on the piano I mentioned, so not that much higher. I start to feel the strain after about 1½ hours. The best position is to have my heel flush with the pedal when it is up.
Well, that's certainly higher than average (what piano is it, by the way?) but it's still not immense, especially compared to the length of heel that Yuja is seen wearing which would be well above pedal height, this requiring her to force-flex her ankles unnecessarily in order to depress the pedals. Again, it's not just the height issue but also the fact that spindly stilettos are by definition far harder to manage pedalling with than the couple of books that you use with the piano that you mention - and as for controling half-dealling / half-damping in them, well, I think that this would speak for itself!
Also, I mentioned, I've never encountered a male pianist who would do this or feel any necessity to do it, yet I cannot see why it would be an issue for certain female ones. Why suffer unnecessary ankle strain when there are enough difficulties already without adding to them!
Best,
Alistair