Glenn Close has a terrific voice with a LOT of power behind it, and a decent range. Catherine has neither of those things.
And The Witch isn't impossible to sing...and I'm not talking about it being high or low (much lower keys has nothing to do with my point) - she simply does not have the technique, power, breath, OR range (acting, vocal, or otherwise) to pull off The Witch.
Mame is more up her alley. APPLAUSE is more up her alley. She might even justify bringing THEY'RE PLAYING OUR SONG back to Broadway.
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson