Maria would enter a convent
So Maria and Joe are clearly references to Mary and Joseph in the Bible. Like Mary, Maria is a selfless, matronly figure who remains a virgin. Yet in this case, it seems like that choice isn't necessarily a deliberate one with all the references to her being single as almost a failure on her part, or a "mistake" like her mistake in singing. In this way you can kinda read it like the oppressive nature of the Catholic Church forcing these roles onto the people, depriving them of living a fulfilled life. Also complicated since in this Maria acts as a mother to Joe, rather than the husband/wife relationship between Mary and Joseph.