From what I understand the Vatican II documents describe her as co-Redemptrix without ever giving her that title because that was the concern at that time, that it would confuse non-Catholics.
The Vatican 2 drafts of the schema did not describe Mary as Co-Redemptrix. There was a booklet dated October 4, 1963 which was circulated by the Servites (Order of the Servants of Mary) suggesting that if the reference to the titles of Mary were to be included in the schema, than an additional title of Co-Redemptrix be included. I have no information as to how widely the booklet was circulated. However, the title Mediatrix Of All Graces was under tremendous discussion as to whether it would be included, and if so, what discussion might be included as to its meaning and extent.
Other than the booklet (which was not a part of any version of the schema), the term was not used in any versions of the schema.
Cardinal Silva Henriquez of Santiago de Chile, in addressing the Council and speaking on behalf of 44 Latin American bishops said that the devotion to the Virgin Mary in those countries at times went beyond the bounds of Christian devotion.
The whole approach to how the Council would address Mary not only included discussion of her titles, but also whether or not the Council would make the discussion of Mary into a separate document or make it part of the document on the Church. But the title of Co-Redemptrix, while discussed outside of the sessions at the various meetings of groups of bishops, was not included in the schemas - in other words, not in depth. The depth appears to have been around the title of Mediatrix Of All Graces, part of the original schema.
One of the points made against Mediatrix Of All Graces was how the Virgin could be the Mediatrix of the sacramental graces flowing from the very nature of the sacraments themselves. In other words, rather than be a benefit, it would result in much confusion. In the final document, “of all graces” was removed.
In the document the Dogmatic Constitution On The Church,
Lumen Gentium, paragraph 62 sets out her titles (with a footnote to documents and speeches of Popes Leo XIII, Pius X, Pius XI and Pius XII) in Vatican Council II vol. 1 revised. She is referred to as “Mediatrix”.
As to whether it was a concern about confusing non-Catholics, or both they and Catholics could be debated, sourcing any materials from the numerous bishops’ conferences and floor discussions at the Council. I suspect that there was concern for all, Catholics and non-Catholics as the issue “of all graces” can illustrate.