Fluttershy song! This fits her so well. And I'm not the first person to think that lol!

Applejack - Alto 2 (Lowest part)
*Percussion
Twilight Sparkle - Alto 1 (Second Lowest Part)
*Bass line
Rainbow Dash - Soprano 2 B (Third Lowest Part)
*Low Ahhs/Low Melody
Pinkie Pie - Soprano 2 A (Third Highest Part)
*Instrumental Melody
Rarity - Soprano 1 B (Second Highest Part)
*High Ahhs/High Melody
And Fluttershy - Soprano 1 A (Highest Part)
*Lead Vocals