All the Fathers of the Church say clearly that She (Mary) is co-redemptrix with Christ in the work of our salvation. Saint John Eudes, page 135, The Priest, His Dignity and Obligations.
There are two interrelated doctrines. On this page is discussed Mary as cooperator in the Redemption, Co-Redemptrix, or as some say Coredemptress. The other doctrine, which is related is Mary as Mediatrix of all Graces.