Tell us what those powers are. Is she omnipotent, omniscience, or omnipresent? She would have to be one of the above to be able to hear all prayers at all times.
If you can't answer this conclusively then it would appear that her mediatrix ability is a deduction of your theology...
Since Mary has been glorified by God - that is, since she has been made like our first parents before the Fall, she possesses qualities which are lacking to us.
She has the additional privilege been removed from time and placed into eternity, since saints no longer dwell in time.
She can, like other saints, view time as it were from the outside and also view the actions of her fellow creatures in time as a completed reality.
This knowledge is given to her and to all the blessed by the indwelling of the Holy Spirit. Simultaneity causes no confusion for her - we are bound by constraints of time and space, she isn't.
The distinction between God and the blessed is an enormous gulf - just because the blessed can view all time and all space does not mean they can create it. It does not mean they can alter it or change it by their own power. They can be given knowledge of everything God has created, by the power of the Holy Spirit - but they cannot conceive the mind of God.
By human standards a saint would probably appear to be omnipresent, omniscient and omnipotent - but they are only able to be in the places, know the things, and have the power that God permits them to have.
Mary can be very much more powerful than we are without ever approaching the status of anything other than a mere creature.