Clara Thorn, the witch that fought

It's been a year since Clara's magic manifested itself and she was accepted into Linginbaum's School for Magic Users ("witch" is such a dated term). She's made friends, learned new spells, and most importantly begun to master her unique, once-in-a-generation type of magic: mathemagic. To Clara, all the magic in the world is a mass of glowing, rainbow-colored mathematical equations that she can alter and manipulate. She's used her special ability to raise new and lasting Borders between the Ordinary world and Underhill, the secret and fantastic world of witches.
And now a new school term has begun, with Clara and her friends returning for classes. But things take a strange turn when Clara's dream-elf friend tells her that there's just one more Border left to raise-and that this one must go in a mysterious, desolate forest far in Underhill's North, where an inscrutable something awaits.
"Clara shines as a spunky protagonist who is grown-up enough to accept her destiny.... Jones links math and magic in a way that makes math seem cool.... Fresh ideas, some welcome diversity, and memorable character work enliven the material." -Booklife review of Clara Thorn, the witch that was found.