You can check the FAQ entry about Jesus existence here

Most of what can be said about the historical existence of Jesus can be said about Mary. Short answer : We do have some non-christian sources talking about Jesus (and therefore his family), but none are 100% reliable. So, for Mary, I would say it's as debatable as Jesus existence, although if Jesus existed, he did have a mother, named Mary or not. The name "Mary" (more accuratly, Maria) existed before that, so it's possible.