As he ticks through names she recognizes (but only from the books she's read), Charlie grows more and more excited - also nervous, but let's face it, she was full of nerves right now anyway - and

"Sounds like they have enough to form their own band." Images of angels rocking out on harps float through her mind before she snaps out of it. "Wait, you said Michael, right?"

She'd heard him, so she knows he did indeed mention Michael but she just needs the confirmation so she can properly freak out. Michael in an enclosed space with Dean can't be good news.

Also considering Michael was hell bent on doing the Apocalypse mambo with Lucifer means he was down with destroying her world, and Charlie is totally not okay with that business.