I think Flurry Heart has the potential to become a huge brat.
I don't know, this might be an unpopular opinion, but hear me out:
Essentially born a goddess, capable of powerful magic from birth, adored by everyone around her, and quite literally a "special snowflake," Flurry Heart knew she was unique, even in her early years. Despite her parents' best efforts to maintain some semblance of normalcy in her life, the young princess spent most of her childhood in the public eye. She was showered with praise and adoration at every turn. Delighted by the attention, she spent as much time as she could outside of the castle to interact with her subjects. Much to the excitement and awe of the public, she often displayed her magical talents and her oversized wings, which in her mind were a symbol of her status.
As she grew into an adult, her pride slowly evolved into a feeling of superiority and she soon began to harbor strong feelings of disdain for "common" ponies. Much to the disappointment and despair of her parents, she began to spend most of her time in the castle, content to remain locked away in her luxurious throne room. On the rare occasion that she would make a public appearance, it was only from the castle's balcony, far above the heads of her subjects.
For her throne room, Princess Flurry chose the highest, most well-lit room in the castle for the otherworldly ambience she desired. The sun's rays filtering through her colorful curtains and the clear view of the sky created an impressive atmosphere that left her rare visitors in awe. Her taste in décor reflected her attitude; her affinity for regality was evident with her choices of deep, dramatic reds and golds, though her room still retained some of the jewel-bright colors of her proud Crystal Empire heritage.
In the future, I think she'll overcome these selfish feelings... but only with some help from her Auntie Twilight.
That's the gist of it anyway. Better than a Mary-Sue imho. I'm not much of a storyteller, I much prefer to do it through art, but I thought this one needed some backstory I was partially inspired by this song.
Good god, I really need to practice drawing wings.
Also, did I ever tell you guys that drawing fabric is one of my favorite things to do?
Unfortunately, the possibility is not really unlikely, as much as I don't think it will happen, because Shining Armor and Cadence are not particularly good parents. And not exactly bad ones either (not completely, at least), but it does seem like they are overchallenged with Flurry.