Say hello to Radiant Heart. She's a childhood friend of Mi Amore Cadenza, thought they haven't been in touch for quite a few years, not since Cadence ascended to become an Alicorn and princess.
Her special talent, well, is magic. Unusual for a pegasus to be sure, but she graduated from Celestia's School for Talented Unicorns. After graduation, she became a teacher at that school. She teaches a little about magic, mostly magic theory and history, but can actually use magic such as levitation through her wings.
She is kind and patient with her students, though a little shy around other ponies. She is an average flier, and occasionally helps with Canterlot's weather, mainly around the school.
She is sent by Princess Celestia to Hogwarts to teach Magic of the Heart to the students.