A little old but from a couple of 2007 press releases which mention Polly.
Alison Krauss & Robert Plant: In a dark mood (LA Times)Quote:
.....and PJ Harvey’s “Pocket Knife,” which was recorded but was left off because Krauss wasn‘t satisfied with her performance.
http://www.robertplant.com/press/alison-krauss-robert-plant-in-a-dark-mood-la-times/Don’t Get Mad; Get Heathen! (The Word magazine)Quote:
........Which means that Krauss sounds like the newly high-pitched PJ Harvey when she sings Tom Waits‘ Trampled Rose
http://www.robertplant.com/press/don%E2%80%98t-get-mad-get-heathen-the-word-magazine/