Hi Chris,
I think the small but imprtant distinction is, does the Church call Mary a co-redemptrix, vs. is it a reasonable position to say that “since she had a unique and important singular role in the salvation plan (which is explicitly stated in the CCC), do I conclude she acted as a co-redeemer?” To this question, I think someone could say “that’s a reasonable conclusion you could draw based on your definition of co-redeemer and the part Mary played.”
For me, when the question is asked, I imply the real question is “Does the Church ***title ***Mary as co-redeemer?”, and I think the answer to that is no - it doesn’t exist anywhere that I have seen.