Why didn't Mary ask for the first miracle earlier?

In his commentary on the dialogue between Mary and Jesus at the Wedding at Cana, St. John Chrysostom offers this explanation:

"Now there was a shortage of wine; Jesus' mother said to him, 'They have no wine.' Jesus answered her, 'Woman, what do you want from me? My hour has not yet come.' Jn 2:3-4  

It is important to examine the source of Jesus' mother's high opinion of her Son, when he had not yet performed any miracles, since the Evangelist later remarks: 'So Jesus performed the first of his miracles at Cana in Galilee,' etc.

We reply that his glory and power were beginning to be revealed by the testimony of John, and by what Jesus himself was saying to his disciples. Moreover, and long before that, his divine conception and the prodigies which surrounded his birth had given Mary the highest impression of the child of whom she was the mother. Saint Luke confirms this explanation when he says: 'And his mother kept all these things in her heart.'

Why, then, did Mary not urge him earlier to perform miracles? It was because he was just beginning his public life; until then his external life had been that of an ordinary man, and his mother had not dared to make a similar request. But as soon as she heard the testimony John had given of him, and saw him surrounded by disciples, she prayed to him with confidence.

Translated from Marian Enciclopedia