How can Mary be the Mother of God?

Jesus is God, but Mary is not the mother of God; she's the mother of the physical body Jesus was incarnated into. I'm surprised you don't know that all of the Christian church, both Catholics and Protestants, believe that Jesus is God. There is one God in three persons: the Father, Son, and Holy Spirit. It's not easy for us to comprehend in our finite minds how God does this, but it's what the 'Bible teaches. Don't try to use human reasoning to reason it out.