“I know it’s not enough to undo what I did to you, and to the entire school, but with all my heart I ask for your forgiveness.
Now I understand why you used the Memory Stone, Wallflower Blush, and I don’t blame you; I wasn’t exactly a ‘model princess’ back then, but now that we are friends I will do everything in my power to help you.”
You know, if they did show Sunset bullying or doing something really nasty to Wallflower like in this pic, I could easily accept her wanting revenge as opposed to her just taking her problems out on Sunset for no reason.
Sunset probably did bully Wallflower at one point, then after getting reformed via rainbow laser tried to apologize to her only for Wallflower to use the memory stone on her, thus erasing any memory Sunset had of even meeting her.
“For you, the day Sunset Shimmer killed your daisy was the most important day of your life. But for me… It was Tuesday.”