A quick search did show lots of references between Voodoo and cleansing of spirits. I thought it was in a Christian church hymn as well, but that is “Create in me a clean Heart”. Although I imagine there are references in the Bible to folks with a clean spirit.
Quite different from 'clean spirits' hanging around.
Somebody close to Michelle is practicing voudou, santeria, or wicca. They're the only ones that talk about "clean spirits".
Or maybe she's just a New Age nut that's been reading too much gobbledegook.