God bless!
We have spoken already of two great Pillars of Orthodoxy-using similar expression:
St. Gregory Palamas ( he often wrote about her as the Mediatress of all that is good)
St. Theophan the branded
Then I posted some short quotes of St. John of Damascus !
the benefactress of all creation as a repayment of our debt.
Hail, inexhaustible ocean of grace
She is the channel of all our blessings.
For our sake she became Mediatrix of all blessings, in her God became man and man became God.
If we firmly abstain, then from past vices annd love the virtues with all our hearrt, taking them as our companions in life, the Virgin will frequently
visit us bringing all manners of Graces.
O daughter of Joachim and anna, O mostholy Lady receive the word of a sinful servant, who nerverless burns wiwth love and places in you his only hope of joy, in you he finds the guardian of life, not only a Mediatrix in your Son's presence but a sure pledge of SALVATION.
She is all beautiful, all near to God. For she,surpasses the cherubim, exalted beyind the seraphim,
is placed near God.
St. Andrew of crete:
O how marvelous it is ! She acts as
mediatrix between the loftiness of God and the lowliness of the flesh.
O mistress of all man oh thou provider of life, life of the living, O holy One, holier without compare than all the Saints,
supremly holy treasury of all that makes us holy....All creation is
full of thy Glory,all things
are made holy through thee,...all universe owns u as its common Altar of cleansing sacrifice...aside from God you are the highest being...
St. Cyrill -every good gift comes from God through the Theotokos:
Through you the Trinity is glorified, the precious cross is celebrated and adored thoughout the world, heaven exults, the angles and archangles rjoice, the demos are put to flight because of you the devil the tempter falls from heaven, the fallen creation is brought back to paradise.....
Through you holy baptism and the oil of gladness are administered !!!!!!!! to the believers, through you the churches are established throughout the world, the people are led to conversion through you. What more shall I say ???????
Through you the Trintiy reigns......!!!!
Through you, every faithful soul achieves the Salvation.
St. John of Thessalonica:
The mistress of the whole universe,
through her all creation has received Salvation.
She is
the Benefactress of the whole world....She is only second to the Trinity, we shall show worthy of
all HER gifts......
She has free access to God and bestows on us the spiritual gifts,
she gives grace to our words, she teaches wisdom, She is the Mother of wisdom....she bestowed upon the world the price of peace....While she lived on earth, she watched over us all, and was a kind of universal providence for her subjects. Now she has been taken up into heaven,
she is the unassailable fortificatiion for the whole human race, and the intercessor for all.....
St. Modestus_
By the grace that came forth from her, every spiritual and intellectual nature shares eternal life.....Since u abide in his presence with full freedom of acces....paradise is given to the Saints
through your Mediation....so that through you he might open up for us a means of acces to him......
and we have gained the gifts of the Spirit and eternal blessings through you.........
St. Germanos:
O Mother of God because of you...it is that the human person is now made a full citizien of heaven
through your immacualte flesh.....
No one is saved except through you, O All-Holy One, No one is delivered from evil except throgh you O All chaste One,
No one obtains the grace of mercy except throgh you O All-honorable One.....
She is the Mediatrix of all sinners...
St. John of Kronstadt:
She is the highest of all creation,
She is the Mediatrix for the whole human race......
she prepares eternal glory for us......Our Lady the Mostholy Mother of God is the most beautiful adorned Temple of the Trinity,
She is after God the treasury of ALL BLESSING, of purity holiness, of all true wisdom, the source of spiritual power and constancy.
St. Theophan

already written)
The Mother of God is the Dispenser and Distributer of all the wondros uncreated gifts of the Divine Spirit....she distibutes it and shares with others thus manifesting it..... All things were created for her and
are goverened through her. No one attains the goal of life in Christ
without her cooperation.....
no one can participate in the divine gifts save through the Theotokos......
I think in these few ( I could go on and on) quotes we can clearly see that every blessing and grace comes from God through her. So it is not contrary to orthodox understanding to call her Mediatrix of all graces, or co-redeemer........ but you are right we do not need any new Dogma !
At Vespers on the forefeast of the Nativity of the Theotokos:
The spiritual beams of universal joy have dawned for the world, at your nativity, O All-pure One, foreshadowing for all the sun of glory, Christ God. For you have been declared
the Mediatrix of the true gladness and grace.
St. Gregory the wonderworker:
For from Mary, the divine fountain of the ineffable Godhead,
gushes forth grace and free gift of the Holy Spirit... because with her are quickened and live,
all the treasures of Grace....
IN CHRIST