Oh jeez what a sappy title, spot on, but very sappy.
As far as I am aware it has never been made clear which wing Glory loses. (Honestly I've forgotten, tried to look it up and failed)
But every time she blocks Scotch Tape's view I always pictured she did so with her left wing.
Best part was when they visited the shop of "Velvet" ( awesome ask-tumblr reference in the story -> [link]
) and she somehow got out with some toys! (yay!)
Aaaaalmost gave her Fluttershy eyes.