Please read carefully: God pre-existed Mary, He is eternal, He has no beginning and no end. God is Mary's Creator. And yes, God has no mother. If God has a mother, than God has a beginning. To say that Mary is the mother of the divine (God) is to suggest that she pre-existed Him. A mother always pre-exists her offspring. (Obviously). God pre-existed Mary and is from everlasting to everlasting. The incarnation is in many ways a mystery and can be difficult to adequately understand or explain, but this we know: Jesus was fully God and fully man. His divinity and His humanity are not separate and yet, His divinity (as God) is eternal and did not originate with Mary. As a man Jesus had an earthly mother, as God, He does not. (And this is clearly true because we know from Scripture that God always existed and He created Mary. She, like all of us, has a beginning, God does not.)