I got that one quickly through an apparent glitch. See post below(somewhere down there).
I can't believe this... I figured this out just a minute before I saw you'd posted a hint, because someone else mentioned what room to use. But I'm annoyed at myself it took so long because I've used every game mechanic this required repeatedly to solve other stars and secrets, and yet every time I looked at this one I just kept thinking "but, my cat will turn to stone, so I can't come in that way". /facepalm