So, of all the things Trads are focused on, this really is one of the least horrible things the Modernist have done. I know there's a lot of emotional attachment to Our Lady, but it would not somehow be to dishonor Our Lady if we were to, say, not grant her the title of Fourth Person of the Holy Trinity. In fact, erroneous titles only dishononr her.
There were PRE-VATICAN II THEOLOGIANS, approved and respected, cited by the Dimond Brothers, who also said that the title of Co-Redemptrix is problematic, confusing, and potentially mis leading, and "best avoided".
Now, one might RIGHTLY be cynical that this is the motivation of the Modernist heretics, to avoid confusion, since Bergoglio practially reveled in it, bragging about how he liked to cause messes, and the confusion of Fiducia Supplicans they felt was easily addressed by putting in a sentence of explanation about how it's not to resemble a marrige in any way and that the relationship wasn't being blessed, just the individuals.
Now, the title is defensible, but I have not yet seen a Trad actually defend it theologically against the objections that have been brought against the Title, but merely rend their garments and virtue signal about how much they're devoted to Our Lady and all that.
I believe the title is not only defensible, but very apt, and should be bestowed upon Our Lady, and the necessary distinctions easily explained in a sentence or two alongside the proclamation ... so I disagree with the Dimond Brothers, but as of this time no one has properly defend the title from a theological perspective. I will do that myself when I have time.