Is Mary the Mediatrix of All Grace?

In Ephesus Christ is the cause of all grace in the entire history of salvation and Mary is in a way the instrumental cause of Christ humanity. So therefore she really is a, I mean, if she had done nothing else than just say yes to the angel at the enunciation, she would be that cause in us. But she also has this special intercessory role at the further cross and then at the throne of God in heaven such that some of the saints have even said that Mary has her intercession has a certain omnipotence so to speak. She wouldn't ask anything other than what the Lord wishes to grant us.