But the key difference is that Luther did not consider her to be a co redemptrix.
Neither do Catholics.
Bingo--or as Luther would have put it, "Volltreffer!"
I had a big issue with this doctrine when I first heard of it. Apparently, co-redemptrix literally means “with the redeemer” the doctrine refers to her remaining with Jesus (i.e. sticking by his side) throughout her life. It is not, apparently, supposed to be interpreted in the same fashion as more common terms like “co-owner” that assumes an equal partnership.