The emphasis of the Rosary is on Jesus' life and trials during his physical presence on earth. (I jumped in the middle of something here, so my apologies if my answer doesn't address what you were asking.)
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Personally, I don't care much for the term Coredemptrix because of the impression it gives. However, it is a Latin word and it must be remembered that the "co" does not mean "equal to". In Latin it has its roots from "cum" which means "with".
Catholic belief is that "Jesus Christ, as true God and true man, redeems the human family, while Mary as Coredemptrix participates with the Redeemer in his one perfect Sacrifice in a completely subordinate and dependent way. The key word here is "participates" in that which is exclusively true of Jesus Christ."
Coredemptrix does not mean that Mary is an equal to Jesus but refers to her free, active, intimate, and unique participation with her Son in his work of redemption (she persevered with him from his conception to his resurrection). I repeat: her role is subordinate to Jesus' and she herself was redeemed by Jesus. Catholics also believe that all Christians are called to offer their suffering to the Father, as brothers (oh no, not this again) of Christ and members of the Body of Christ. And, therefore, we are also co-redeemers.
Although the concept is Catholic belief, the title of Coredemptrix itself is pretty controversial within the Church, and I don't believe it is even official doctrine.
I took the liberty to paraphrase most of this from several documents but I am not an expert on the subject. Maybe someone more knowledgeable, like dignan3, can shed some light on it if you are interested.