Roman Catholic is an old slur in the English language to refer to the Catholic Church first used by the Anglicans who styled themselves Catholic but not Roman. Secondly, your question sounds like a Protestant refusal to accept the dogma of the Church which named the Blessed Virgin Mary as the Mother of God in A.D. 431 at the Council of Ephesus. read more
From antiquity, Mary has been called "Theotokos", or "God-Bearer" (Mother of God). The word in Greek is "Theotokos". The term was used as part of the popular piety of the early first millennium church. It is used throughout the Eastern Church's Liturgy, both Orthodox and Catholic. read more
Second, Ephesus affirmed that our Blessed Mother can rightfully be called the Mother of God: Mary is not Mother of God, the Father, or Mother of God, the Holy Spirit; rather, she is Mother of God, the Son– Jesus Christ. The Council of Ephesus declared Nestorius a heretic, and the Emperor Theodosius ordered him deposed and exiled. read more