Most prayers to Mary are asking her FOR things, not asking her to pray for us.
It's easy to see wit ha quick google search and decent reading comprehension.
"Holy Mary, mother of God, pray for us sinners, now and at the hour of our death" is the conclusion of the most common Marian prayer, the Hail Mary. And most prayers asking people to pray for us are also asking to pray for things--for example, "Pray also for me, that whenever I open my mouth, words may be given me so that I will fearlelessly make known the mystery of the gospel, for which I am an ambassador in chains." (Ephesians 6:19-20)