Prayer is part of worship; hence when Catholics pray to Mary they are worshiping her.
We know she is a human being who has Jesus as her Savior, and is a handmaid of the Lord.
Glad you acknowledge Mary is a sinner and in need of a Savior.
Now realize that this is basic Catholic doctrine!
The word "pray" in its original and most authentic sense, is only encountered in three places in America today:
In a court of law ("The appellant prays this honorable court...")
In Shakespeare and other Elizabethan-era authors ("I pray you, do not fall in love with me")
and in Catholic intercessory prayers.
But here's a Biblical example:
Luke 14:18 "And they all with one consent began to make excuse. The first said unto him, I have bought a piece of ground, and I must needs go and see it: I pray thee have me excused."
This is how we pray to Mary and the Saints: "Pray," as a request...
If I say "Please say a prayer for me," I'm praying to you!
But even if you wear a hat that makes you look "adorable" .... I don't adore you!
It is a teaching of the Catholic Church that Mary was conceived without Original Sin (the Immaculate Conception) and remained sinless throughout her life.
She was the only human born of two human parents in history to be entirely sinless.