There does seem to be some controversy when we speak like this about Mary and the other saints because it seems to conflict with what St. Paul says to Timothy.
1 Timothy 2:5 For there is one God, and one mediator also between God and men, the man Christ Jesus.
So some people give us the objection of, “You all are going to the saints and Mary instead of going straight to God, which St. Paul is telling Timothy we need to do.”
We need to answer this objection by pointing out the context of 1Timothy, Chapter 2. Look how St. Paul tells Timothy to intercede on behalf of certain leaders for their ultimate salvation.
1 Timothy 2:1-4 First of all, then, I urge that entreaties and prayers, petitions and thanksgivings, be made on behalf of all men, for kings and all who are in authority, in order that we may lead a tranquil and quiet life in all godliness and dignity. This is good and acceptable in the sight of God our Savior, who desires all men to be saved and to come to the knowledge of the truth. For there is one God, and one mediator also between God and men, the man Christ Jesus.
So St. Paul is asking Timothy to pray to God on behalf of a third party. That is what we are doing with the saints in Heaven, asking them for their prayers.
Before we proceed any further, we should find if there are any verses that suggest that one person can be a mediator of grace for another person.
Well, the ultimate example of this is Jesus HHimself who is a Man who received grace to give to the whole world. But St. Paul speaks of this in his letter to the Ephesians:
Ephesians 3:1-2 For this reason I, Paul, the prisoner of Christ Jesus for the sake of you Gentiles-- if indeed you have heard of the stewardship of God's grace which was given to me for you;
Ephesians 4:29 Let no unwholesome word proceed from your mouth, but only such a word as is good for edification according to the need of the moment, that it may give grace to those who hear.
So we can ourselves be mediators of God’s grace.
So then specifically with Mary, the Mother of Jesus, are there any times that we see her being a mediator?
I think there are at least three occurrences recorded in the Bible for us to ponder and each time they occur it is when Mary speaks. She only speaks four times in the Bible and three of those times it is pretty clear that she is speaking as a mediator.
Where is the first time?
The first time is at the Annunciation where the Archangel Gabriel comes to Mary on behalf of God the Father to see if she would be Mother to the Redeemer of the World. She, of course, accepts and on behalf of the whole world brings Jesus into it.
Is Mary ever a mediator for the Holy Spirit?
We see this when Mary visits Elizabeth her cousin.
Luke 1:39-44 Now at this time Mary arose and went with haste to the hill country, to a city of Judah, and entered the house of Zacharias and greeted Elizabeth. And it came about that when Elizabeth heard Mary's greeting, the baby leaped in her womb; and Elizabeth was filled with the Holy Spirit. And she cried out with a loud voice, and said, "Blessed among women are you, and blessed is the fruit of your womb! "And how has it happened to me, that the mother of my Lord should come to me? "For behold, when the sound of your greeting reached my ears, the baby leaped in my womb for joy.
It is specifically at this moment that the Archangel Gabriel’s words to Zechariah are fulfilled when the angel said to him:
Luke 1:15 15 "For he will be great in the sight of the Lord, and he will drink no wine or liquor; and he will be filled with the Holy Spirit, while yet in his mother's womb.
This is the moment when St. John would receive the Holy Spirit, yet while still in his mother’s womb (good argument for infant baptism by the way). But what prompted his reception of the Holy Spirit – Mary’s greeting. Mary here is a mediator for the Holy Spirit.
The last one is obviously the wedding at Cana.
Yes, in John chapter 2 it says this:
John 2:2-5 3 And when the wine gave out, the mother of Jesus said to Him, "They have no wine." 4 And Jesus said to her, "Woman, what do I have to do with you? My hour has not yet come." 5 His mother said to the servants, "Whatever He says to you, do it."
Mary intercedes for the wedding party with her son who not only performs his first miracle with such splendor but it is a miracle that points us ultimately to the Cross where Jesus would make all mediatorship in him possible.