Yep, I remember that bit, and it was in reference to Illume, not the Phoenix Four
I couldn't really imagine that, as damn good as those songs are. (Hmm... Say You Will, Illume, DR ... what's the next one? Not Silver Girl??
)
Meanwhile, personally I'm surprised that not everyone who listened to Illume for the first time had a tear in their eye and thought 'How did she do it'. Stevie and the band were never going to release a song directly referring to 9/11. Except obviously the title directly referred to it, which still surprises me. But the song itself is an ethereal dirge about massive grief and trauma, being scared witless, being haunted at night...
One of my favourite lines goes something like 'When you haunt us, just remember that I was so scared' ('I was so scared' I read as sort of meaning 'I was levelled by sympathy for you'). It's that idea of being haunted that I assume inspired Lindsey to do that ghost voice. I get the impression that it ruins the song for some people because it stands out too much, whereas for me it just takes the song to an even deeper level. Plus, in terms of arrangement/production, it sets up Stevie for that awesome refrain sung in a higher, louder register. When she sings that, it's like she's shouting down the ghost, and by the end of the song it sounds like she's lulling into peaceful sleep, like she's successfully dealt with her demons. I love it!