She is still understanding what Jesus has said as if it applied to the physical realm and not the spiritual, much in the way Nicodemus did the new birth.  It would be convenient for her to not have to come and draw water, so if this man can truly give this, she will ask him for it, though she probably doesn’t think he can really do it.

However weakly, she has indeed responded positively to the statement Jesus said to her, with the purpose of engaging her in a much deeper conversation. It is as if Jesus was casting the bait before the fish, and it (she) had come and nibbled at it as He patiently waited and now the fish has taken the bait. The bobber has plunged beneath the surface of the water and Jesus is about to set the hook, which He does in the next verse.