Suppose a devout Presbyterian visits a mosque and recites the words printed in that bulletin. The answer to such questions requires not only an assessment of the words but also of what the person saying them believes. God is not a rock, nor an army commander, nor a shepherd, nor a devouring fire, though the Bible uses all these metaphors to teach us about God. As Christians we can pray to the Lord of Hosts or the Good Shepherd. But we should remember that what a metaphor teaches isn't the only thing we know about God.
People give different answers.
Others object that although the Bible may have maternal metaphors for God, it contains no prayer explicitly addressed to God the Mother. The prayer seems clear, devout and Christian even though there is no prayer in the Bible addressed to the Holy Child of Bethlehem. Presbyterian ministers who offer public prayer to Mother God obviously know this will upset many people. If so, then it is not Christian prayer. Yet it may be they are struggling to express genuine Christian prayer in language that is faithful to maternal images of God in the Bible, faithful to their own experience in prayer of God's maternal face, and faithful to their desire to include people whose hearts respond to God's maternal care.