I know streaming isn't the be-all and end-all but it's a pretty good indicator of what is popular right now, so I combined her streams (Youtube + Spotify) and it goes something like this.
-Signature song (800M+): La Isla Bonita.
-Mega classics (200M+): Hung Up, Material Girl, Like A Prayer, Like A Virgin, Vogue, Frozen, Papa Don't Preach, 4 Minutes, Holiday.
-Classics (80M+): Into The Groove, Crazy For You, Live To Tell, Sorry, True Blue, Open Your Heart, Music, Borderline, The Power Of Good-Bye, Express Yourself, Give It 2 Me, Celebration.
-Underrated (40M+): Ray Of Light, Take A Bow, Don't Cry For Me Argentina, Lucky Star, Don't Tell Me, Jump, Dress You Up, Justify My Love, American Pie, Die Another Day, Secret.