Am I going to apologize for these headcanons that I just wrote because they’ll spread some pain? Of course not. I’ll be putting them under the cut because it’s a bit long!
trigger warning: mention of death in the first headcanon.
001.) When Argyle died, Sunny was still a growing filly. It left her emotionally distraught and it was one of the hardest times in her life that she went through. As a result of having no other relatives, Sunny had to take care of herself while growing up. Argyle's death still leaves a strain on her today, especially whenever the anniversary comes up. She's far more quiet than usual when that time comes. The only emotional support Sunny had throughout these times was her foalhood friend and one of her close friends, Hitch. She was never really that close to Sprout.
spoiler warning: taking some inspiration from the episode "ali-conned."
002.) Before magic came back to Equstria, it was known that Sunny always stood up for when she stood up for what she believed in. Sunny never gave up - even if when it came to becoming a laughing stock or being completely ignored. However despite her claims, Sunny started to feel the doubt crawl in and she’d feel small no matter how big her voice was. Things became worse when Sunny became an alicorn, it wasn't hard to notice. Other ponies was startling to like Sunny for being an alicorn and for her heroic acts, not as who she was pass those things. She doesn't want anyone to think she's cool for that. This was when the doubt started crawl in further with anxiety. From time to time, Sunny always finds herself asking one question-- "Are they really my friends" or "Am I really worth something?" Sunny has the tendency to close herself off to everyone else whenever she gets into this state. If Sunny wants to be left alone, she will make it known by lashing out or snapping when she doesn't mean it. This is something she'll never do to anyone.