Flurry Heart, being a natural born alicorn, matures at a faster rate than average ponies. This explains why she could fly, use magic, and do just about everything a newborn shouldn’t be able to do. She was essentially a toddler by the time the mane six met her. When Twilight babysat her, she already had the mental capacity of a five year old. She was able to understand situations and be hurt by them, even though she was hardly a few months old.
Her increased growth rate is also why she’s bigger than normal babies, and why she’s not very interested in playing with other infants. It’ll curb off once she’s out of her actual toddler years.
Her horn is shorter. Let’s be real, there’s no way poor Cadence could give birth to that.
Flurry is emotionally connected to the Crystal Heart. It wasn’t her cry that shattered it during her introduction, it was her distress. She’s the soul of the Empire, and is very in tune to the feelings and wellbeing of her people just as the Heart is.
Despite her royal status, Cadence and Shining Armor have worked hard to give her a normal life. School, hobbies, privacy…She’s not secluded from the public eye, but there are boundaries set to ensure she has her space. Cadence especially was adamant about Flurry having an average childhood, as she also grew up as a royal and understands the pressures that comes with it.
Currently, there are no other beings like Flurry Heart. As an alicorn by birth, she’s truly a one of a kind and each day is a learning experience for her and her family.
I’ll probably add more later. She’s still a filly in this pic since I’m too lazy to draw an adult design for her.