How do you know she was praying to Mary? Were you there listening to her? Were you in her head reading her mind? If not, one would not want to be presumptous to know what someone else is thinking. But if you are that enlightened on your walk and you know what is in others hearts and minds when others pray, well, that is something.
Here is what likely happened, but I won't presume to know. A woman went to a statue of Mary, knelt to pray, and asked Mary for her prayers. Maybe it sounded like this, but I am only speculating, for I don't know, "Hail Mary, Full of Grace, Blessed Are Thou Amongst Women and Blessed is the Fruit of Thy Womb, Jesus" (That sounds a lot like something in the Bible). "Holy Mary, Mother of God, Pray for us sinners now and at the hour of our death. Sounds like she is asking for someone's spiritual support, like one would ask a Pastor or a friend.
My Catholic husband was with me and was surprised. He assumed the same thing I did and found it unusual. That's why I find it incredulous that someone who was not there is lecturing me on what I saw or didn't see.