@Background Pony #7BE8  
Since her backstory diverged from canon after the Rainboom race didn’t happen, it would require canon Rainbow Dash to also be born wingless and also missing a wing secretly. It might work for a fanfic for an alt-universe Rainbow though.

@Background Pony #7BE8  
Hows that for a story?

I just thought she was born without wings and since in the comics you can steal a pony’s wings and use them to fly, I’d figured that she took to wich craft to fly and drank a bit of the potion but had the other pony have the rest. That way they both could fly, and when she realized that in doing so that she’d only ever have 1 wing, she was heartbroken because of the effort she had put into the potion that she had a false wing put on the help ease the grief. And the rest is history

@TheMasterEraser  
That’s a pretty good headcanon ^^ I was always thinking she was saving someone from a magic blast and it teared off her wing and hurt her eye and ear

My headcanon is that she was trying to use the “wind slice” technique we saw from the Wonderbolts in Season 2 when Spike grew big and they shaved his head. She was trying to end the war by slicing Sombra, but he blocked her with a sharp crystal at the last second and sheared off her wing with it.