Secrets of the Silent Witch, Vol. 3 (manga)

Now that Cyril is saved, Monica Everett finally confronts the criminal she's been seeking—the accomplice who helped Aaron O'Brien embezzle the student council funds. Her opponent wields a dangerous and forbidden magecraft that appears to be "perfect," but even that stands no chance against the mathematical genius of the Silent Witch. However, bringing the perpetrator to justice proves to be just the beginning of Monica's troubles, as a dragon and a quirky new classmate burst onto the scene…!

Volume 3 of the Secrets of the Silent Witch manga series by Nanna Fujimi.