Names for a character?

I am struggling to think of a name for the main character of my story. I want the name to be MEDIEVAL and UNIQUE. The girl is 22 and she is wild, reckless but spirited. She has long scarlett hair, green eyes and porcelain skin. I am either going to call her Mya (My-uh), Myla (My-luh) or Mercia (Mur-see-uh) which you can shorten to Mercy. Which one do you like the best? I'm open to any other ideas you might have of medieval names for my character but I'd like them to begin with M.