In the past, it was thanks to him having both telepathic and reality-warping powers that he was able to keep his cover (by making humans see the illusion of his human face) while he was free to indulge in his reality-warping hobby of transforming his head into whatever he wanted, to pass the time (which was probably out of boredom). But the illusion aspect didn't work on her. ...I think he has BOTH telepathic mind control power (to force humans to see illusions, something that isn't there) and reality warping power (to change what is actually there, on a phsyical level, and not just visual illusions): and it's his telepathic power that doesn't work fully with her.
I see, so her seeing his beautiful face is equivalent to him successfully manipulating her mind
The only thing I'm confused about, is how come she's the only one who couldn't see his face in the beginning? If he's an entity that can alter then world and it's existence, why can't his face appear to her? She lives in the world he can reshape and rebuild, which means she can be altered as well (explains the reviving). But I just don't get the face thing, why is she different?