Who did background vocals and co-wrote "Best Days of Your Life"?
Kellie Pickler (album):  Since the albums' release, three more singles have charted; "Best Days of Your Life" at number 9 (which was co-wrote with fellow country artist Taylor Swift), "Didn't You Know How Much I Loved You" at number 14 (a re-recording of an album cut from Pickler's debut album "Small Town Girl") and "Makin' Me Fall in Love Again" at number 30. Best Days of Your Life:  Swift also provides background vocals on the song.
Taylor Swift