That is why the intercessionary prayers of Mary are much more effective. "The prayer of a righteous man are truly effective". Why? Because God's will be done. When a person prays that God's will be done, it is more likely that his prayer will indeed be answered. Thus, since Mary's will is perfectly united to her Son's, we have a powerful intercessor.
Then if there is a pecking order of effective prayer (the righteous get what they want more so than the less righteous), does Mary also discriminate on whether she will pray to God on behalf of less righteous people? I mean, if Mary prays for everyone equally, then that is a skirt around the original rule. Any bum could pray to Mary and get the same result as a righteous man. However, if Mary DOES discriminate, like God does, then why bother going to Mary in the first place if you wind up in the same place? She would be of no special advantage then (if she discriminated).