There would have been no Chair of Peter at Antioch and later in Rome had the Apostle not gone to the Blessed Virgin Mary for forgiveness. That is why Mary is the Co-Redemptrix, Mediatrix, and Advocate for mankind to Heaven as you'll see below.
Mary's Role in Prayer and Forgiveness
A. Statement Of the Catholic View.
Mary is a Mediatrix and Advocate for man to God.
Pope Leo XIII said of Mary: "To thee we lift our prayers, for thou
art the Mediatrix ... of our salvation" - Rosary, p. 121; (cf.
Saint Bernard said: "...the Eternal Father ..., besides giving us
Jesus Christ, our principal Advocate with Him, was pleased also to give us
Mary, as our Advocate with Jesus Christ" - Glories, p. 169
(see also p 127,92,56,84,95,171,162,166,89).
Mary also is Co-Redemptrix with Christ, having power to dispense
forgiveness to sinners as she wills.
"Because of her consent to accept the office of Mother of the
Redeemer, and also because of her merits in intimately sharing the
sufferings of her Divine Son for the salvation of mankind, the Blessed
Virgin is given the title of Co-Redemptrix of the human race" - Baltimore
Catechism, p. 49.
Pope Pius XI said: "[W]hen her beloved Son was consummating the
redemption of mankind on the altar of the Cross, she stood at His side,
suffering and redeeming with Him" - Legio Mariae, p. 170,171.
Her act of submitting to become Jesus' mother was "the most heroic
act ever performed in the world - such that in all ages no other creature
but she could have performed it." Had she refused, "Redemption has
never come on earth for" us. So, "Redemption is the joint gift of
the Father and of Mary" - Legio Mariae, pp. 311,312.
Saint Bernard said: "He has placed the whole price of redemption in
the hands of Mary, that she may dispense it at will." - Glories,
p. 85 (see also p. 84,104,141,3,4,8,13,14,131,127,128).
Mary's mediation is so necessary that we cannot be saved without her.
Pope Leo XIII again said: "Thus, as no man goeth to the Father but
by the Son, so no man goeth to Christ but by His Mother" - Rosary,
p. 58. Again, "'...none, O Mother of God, attains salvation except
through thee; none receives a gift from the throne of mercy except through
thee'" (p. 131).
She is "the dispenser of our Lord's Blood" - p. 129. Again,
God "has no children but by her, and communicates no graces but by her
... and through her alone does He dispense His favours and His gifts"
- Legio Mariae, p. 169.
Saint Bernard said: "...Christ is the only mediator of justice...but
because men...fear the Divine Majesty...it was necessary to assign us
another advocate to whom we might have recourse with less fear and more
confidence, and this advocate is Mary" - Glories, p. 169f.
(See also 170,145,103f).
Saint Bonaventure said: "If my redeemer rejects me on account of my
sins, and drives me away from His sacred feet, I will cast myself at those
of His beloved Mother Mary, and ...she will engage her Son to pardon
me." - Glories, p. 90. "...this great Advocate, who is so
powerful...that the Judge, her Son...cannot condemn the guilty who are
defended by her." - Glories, p. 169.
This concept of Mary's mediation is justified by passages that talk
about God's people praying for one another. Examples are James 5:16;
Genesis 20:7,17; Numbers 14:13; Job 42:8; Ephesians 6:18,19; 1 Timothy
2:1,2; Acts 8:24; etc. - (See Question Box, p, 369).
Catholicism claims to believe Jesus is the one mediator between God and
man, yet they hold views that exalt Mary as close to His level as they can.
And in practice they claim she can do things for people that Jesus Himself
will not do.
Note: The copy above is taken from Gospelway.com/religiousgroups/mary.php and the photo above is from Restored Traditions. It is most fitting that the watermark is still in for we would not have tradition had Peter not humbled himself before the Mother of God. Also the X through the picture is symbolic of wiping out his guilt through a firm amendment by the Apostle.