This is Passionfruit, the only daughter of two very rich and “Important” Canterlot ponies with little time for their foal, but plenty of maids and servants and expert tutors to raise her for them. Though being able to order them around and threaten to fire them made her a very obnoxious spoiled brat, she grew out of this over time and became a more pleasant pony to be around. Mostly. As a filly, failing to make real friends and pushing away those who tried to get closer to her hurt her feelings a bit, but it was overhearing her entourage of Barnacles(hangers-on who only put up with her for her money and status or because their parents said so) openly laughing about what an awful pony she is and how unbearable she can be that made her realize she needed to change. She stopped being a bossy and entitled snooty jerk, but continued to be overly pampered, out of touch with the poorer classes, and often accidentally-insensitive/insulting. But hey, at least she tries to be kind to the very few friends she managed to keep, and at least she became generous with the money of her parents. While badly trying to be a better pony, she once read a comic book she’d bought from another schoolpony for five hundred bits (She assumed that was the price, and who would correct her?) and the comic book was about a hero who uses his great power responsibly, for the good of all. And so, she chose to buy her way into Canterlot’s Duel Academy so she could become a master magician and use the mighty magic she’d been gifted with for the good of all of Equestria. She went on many wacky college adventures with Silver Star Apple and the rest of his squad, she grew a lot as a person, and she graduated with a Master’s Degree in Blessed Magic, a PHD in Blessed Magic, and a Bachelor’s Degree in Healing. She failed to get into the actual Equestrian army upon graduating, despite her overqualification(She claims they told her to her face that she’s so overqualified that she’d make the other soldiers feel bad, and whether you believe that or not depends on how much stock you put in her words VS how much you know about how much the Equestrian Army sucks), so her choices were to join the Royal Guard with the other Equestrian army rejects or study at Duel Academy for a bit longer and become an Instructor for Light Magic. She chose the latter, for she had undergone enough personal growth to become a great teacher.
 
She’s a Twonicorn, an incredibly rare but not unheard-of mutant Unicorn blessed with two magical horns, rather than one. Only one in seven Twonicorns are lucky enough to be able to use magic with both horns, and she’s one of the lucky ones. Each horn can focus magic of different wavelengths and cast spells independently or mix different spells and elements for stronger effects, but both horns draw from the same magical source. While she can cast more spells than the average Unicorn in a minute, doing this exhausts her limited stamina much faster. Also, her mane and tail colours don’t match due to a rare genetic condition. And her eye colours don’t match due to a different but rare genetic condition that’s less rare than the hair thing. If this wasn’t Equestria, a country full of (mostly) universally kind and accepting ponies, she would likely be considered some sort of freak for having three incredibly rare genetic mutations in one body.
 
Her Cutie Mark is two Brilliant Rose diamonds, it means duality and light, and it makes her good at casting two beneficial spells at once. Not quite as talent-enhancing as a Cutie Mark in magic itself, but not far off.