Background Pony #A731
My headcanon says Sunset had a twin and Celestia found them in the Frozen Norths as very little children .So I cannot except this headcanon as my own
When Celestia decided to adopt little Twilight, Sunset was livid with her mothers decision. She thought that she was replacing her baby sister who was killed in a terror attack a month before. Sunset did not accept Twilight as her sister and would secretly abuse her whenever their mother was not around.
Well that was Sunset’s initial relationship with Twi and the sling is not Sunset’s doing, she got it from a gunshot wound before she was adopted