A lot of Protestant antagonists insist, against the history of language, that "co" must mean "equal", and so they are scandalized. That's one reason I personally hope it remains loose talk. The theology stands whether or not it is made in any way official.
Never heard a word about the Blessed Mother being *co-redemptrix*.
I have heard and read about the Blessed Mother being *co-mediatrix*. I concur with you on *co must mean equal* nonsense. Words mean things no matter how hard we might wish them to mean something else.