According to J. Duncan M. Derrett in “Water into Wine,” (Biblische Zeitschrift, Neue Folge, 7 (1963), pp. 84-85,89) Mary was deeply concerned about the shortage of wine in John two for a few reasons:
First, she was deeply involved in the preparation for the festivities.
Secondly, the lack of wine at the wedding would be the cause of general disruption.
Thirdly, there would be obvious embarrassment to the host family.
Finally, there was a possibility of legal action against the family.
The lack of wine could be the source of legal action! Not only does wine cheer the heart, but it also keeps you out of legal problems. To not provide for the guests of the wedding would be the ultimate insult. But we also know that wine is a sign of kingship. When one is invited to the feast, he joins the royal gathering and drinks what kings drink. Finally, we must keep in mind that in God’s house wine is never lacking, for He prepares a feast for kings and queens every time we gather to praise Him.
Resurrectio et Vita 