She is more powerful than God himself for even He cannot resist her request.
Not the romantic, are you!
Would it not be unreasonable to argue that God takes great pleasure in granting His children, particularly through the Mother of His Son, their petitions and requests?
Read the psalms.
Because God answers some prayers, but not others. If you pray for the lotto numbers to hit so you will become rich tonight, you probably won't get your wish fulfilled. But if you pray for the strength to work hard, or for the will to overcome your fears, or for the right decision about something, then you stand a better chance of it being granted.
Otherwise I can convert to Catholicism and pray to Mary to get God to make my lotto numbers come up tonight and I will be rich tomorrow as "what she asks, she obtains" and she wouldn't deny my wish would she?