There would not be two girls in the one family called Mary.

The Catholic Answers

There certainly could be. And St. John, XIX., 25, writes that there stood by the cross of Jesus “His mother, and his mother’s sister, Mary of Cleophas.” But even here, Mary of Cleophas need not have been a sister in the first degree of blood relationship, but rather of the same lineage in more remote degrees of either consanguinity or affinity.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty