If a Protestant comes up to you and asks: Why do Catholics pray to Mary? She’s dead.
(say to the Protestant

Do you believe in life after death? We Catholics believe that Mary, along with everyone who left this earth in God’s grace, is in Heaven with Jesus; they aren’t dead anymore - indeed, they are more alive now than they ever were when they were here on earth.
There’s nowhere in the bible that says you can pray to people or ask them to pray for you who aren’t alive.
That’s true - on the other hand, we see Jesus talking to Elijah and Moses, recorded in Matthew 17:1-8; Mark 9:2-8; Luke 9:28-36, and in II Peter 1:16-18.
Jesus also teaches us that since the God of Abraham, Isaac and Jacob is the “God of the living,” this must mean that Abraham, Isaac, and Jacob are experiencing life after death.
Matthew 8:11
I tell you, many will come from east and west, and will sit at table with Abraham, Isaac, and Jacob in the kingdom of heaven,
Matthew 22:32
I am the God of Abraham, and the God of Isaac, and the God of Jacob? He is not the God of the dead but of the living!
Mark 12:26
But concerning the dead being raised–have you not read in the book of Moses, [in the passage] about the [burning] bush, how God said to him, I am the God of Abraham and the God of Isaac and the God of Jacob?
Luke 13:28
There will be weeping and grinding of teeth when you see Abraham and Isaac and Jacob and all the prophets in the kingdom of God, but you yourselves being cast forth (banished, driven away).
Luke 16:23
And in Hades (the realm of the dead), being in torment, he lifted up his eyes and saw Abraham far away, and Lazarus in his bosom.
Luke 16:24
And he cried out and said, Father Abraham, have pity and mercy on me and send Lazarus to dip the tip of his finger in water and cool my tongue, for I am in anguish in this flame.
Luke 16:25
But Abraham said, Child, remember that you in your lifetime fully received [what is due you in] comforts and delights, and Lazarus in like manner the discomforts and distresses; but now he is comforted here and you are in anguish.
Luke 16:29
But Abraham said, They have Moses and the Prophets; let them hear and listen to them.
Luke 16:30
But he answered, No, father Abraham, but if someone from the dead goes to them, they will repent ( change their minds for the better and heartily amend their ways, with abhorrence of their past sins).
Luke 20:37
But that the dead are raised from death]–even Moses made known and showed in the passage concerning the [burning] bush, where he calls the Lord, The God of Abraham, the God of Isaac, and the God of Jacob.
John 8:39
They retorted, Abraham is our father. Jesus said, If you were [truly] Abraham’s children, then you would do the works of Abraham [follow his example, do as Abraham did].
John 8:40
But now [instead] you are wanting and seeking to kill Me, a Man Who has told you the truth which I have heard from God. This is not the way Abraham acted.
John 8:52
The Jews said to Him, Now we know that You are under the power of a demon ( insane). Abraham died, and also the prophets, yet You say, If a man keeps My word, he will never taste of death into all eternity.
John 8:53
Are You greater than our father Abraham? He died, and all the prophets died! Who do You make Yourself out to be?
John 8:56
Your forefather Abraham was extremely happy at the hope and prospect of seeing My day (My incarnation); and he did see it and was delighted.
These verses are from the Amplified Bible.
If they attempt to bind and gag Mother Mary, ask them what they think their own afterlife will be like, and point out to them that Mother Mary has the same freedom right now that they anticipate themselves to have, when they themselves go to Heaven.
I hope this helps.