Secrets of the Silent Witch (Dub)

Monica Everett, the Silent Witch, is the only mage in the world who can use unchanted magecraft, a true hero who singlehandedly defeated a legendary black dragon. However, this young genius is actually…super-duper shy! That's right: She learned to cast spells silently just to avoid speaking in public, and despite her power, she has zero self-confidence. Now Monica has been tasked with secretly guarding the second prince. Can she keep it together as she faces both the evil forces targeting the prince and the terrors of social interaction?

(Source: Yen Press)
Silent Witch: Chinmoku no Majo no Kakushigoto