That is a preposterous myth, like “Pope Joan.”
Pope JP II had a commission study whether Mary should add co-Redeemer and co-Mediatrix to her titles. Francis is studying something similar. There were similar things under consideration in the 19th century. You underestimate the fervor of the Mary devotees. I think that is why the Gospels minimize the role of Mary after the birth of Jesus. Marian devotion can easily get out of hand.