From the text, we do not know that Mary knew then, at the time just previous to the miraculous water-into-wine occurrence, that that was what was going to happen.
If we are to be assuming possibilities, then going by the text, we can as well assume she [Mary] was simply relating what was in her view a sad state of affairs. Not enough wine for the wedding party.
From Christ's own reaction to her (with all of this most likely related to Christ's disciples some time after the crucifixion, and probably the Resurrection too(?)) there can a sense gained that she did know, then, that something significant was about to occur, leading her to say "what ever he says, do that".
To now rely upon that as being how we need approach God, like either household servants, or guests of the wedding party, needing to take instruction from his own earthly mother, Mary, to take instruction from Christ --- flies directly in the face of the "Our Father" explicit instruction which HE gave, as how to best pray.
The earliest church did not direct anyone to pray to "Mary", either, although they may have included some thankfulness and loving remembrance for her having lived --- even among them (for a time).
But praying to her? That is one of those types of practices (and ways of thinking) that crept into the church, over an extended period of time.
So what now? There will be someone just itching to post --- but we only ask her to pray for us"? Uh-huh. Yeah, right. It's not restricted to just that, in all quarters of Romish Catholicism, for she has become as demi-goddess diety, part of a pantheon of angels and saints one is encouraged to direct prayers towards.
I do wish people would stop taking that passage from John 2 out of context, then adding assumption to it, to reach for justification of praying to Mary (or any other) instead of simply praying as Christ more explicitly directed. Our Father, who is in heaven, hallowed be thy name. Thy kingdom come, etc.
Oh wait. Now the itch to make mention of "Mary" as "Queen of Heaven", so as to provide explanation for her being "Queen" of that "kingdom come" which we are to seek the Lord concerning -- which means we should pray to her too.
I know that itch is out there -- just admit it. Any way it can be done, hyper-veneration of "Mary" is promoted as some on-going spiritual necessity, even in the face of direct leading away from "venerating" her for sake of her being the womb and paps which bore His own earthly incarnation.
I've seen all the Marianist arguments before...and they all have one thing in common. They suck.
Just a quick point:
The veneration of the Blessed Mother is called hyperdulia, not hyper-veneration.
The veneration of the saints and angels is called dulia.
The worship of God is called patria.
From the the Hail Mary: "Holy Mary, Mother of God, pray for us sinners...
Catholics are asking Mary to pray for us. Who do you think Mary is praying to?