Who was the singer of the cover of "I've never been to me" that is heard in Shrek The Third during the scene at the "Poison Apple"?

In Shrek The third, there is a cover of "I've never been to me" by Charlene sung by a Witch character in the "Poison Apple" pub, but the singer seems to be unknown. It's not the original version by Charlene, and many websites credit the singer as "Nancy Wilson", but different websites link different singers with that name. While there is a singer named Nancy Wilson who covered the song in 1977, This isn't the same version heard in the movie Here is that version, Wikipedia links this singer as the singer of the version in the film, and IMDB links a different Nancy Wilson as the singer, (a member of the band Heart), I think it's unlikely that Dreamworks had her record a cover of the song to be used for less than a minute in the film and never included it in the Soundtrack album. Some other possibilities are another non-famous singer also named "Nancy Wilson", or an uncredited actress.