Dear Ms. Kunin,
Thank you for these very interesting communications and, of course, for the kind words.
But you perhaps do not know that Sirin actually appears, together with Alkonost, in Rimsky-Korsakov's next-to-last opera, The Tale of the Invisible City of Kitezh and the Maiden Fevronia. It is a beautiful scene.
All good wishes, R Taruskin