"Where do nuns come from?"
Nuns are not and never have been ordained. Only Protestants ordain women. There were, however, women deaconesses who were consecrated in a particular way which distinguished their position from that of the sacramental/liturgical priestly orders, in the early Church. The Synod of the Church of Greece has determined to reestablish this role for women quite recently.
***Only Protestants ordain women.***
Try again.