She knows that without a vessel it is impossible to draw water from the well. She recognizes that it is humanly impossible for anyone to give living water and that in fact without a vessel, Jesus wasn't even able to draw water from the well itself. While, in the natural, all her eyes could see was His lack of a vessel, and the impossibility of 'living water' happening; there was also a part of her that responded to the hope He offered. He had sparked a need that also caused her to acknowledge, that maybe? Maybe there was a vessel? Maybe there was a way?
I love that and even though she doesn't yet recognize the she is looking at and speaking with the vessel that makes 'living water' possible she does recognize the desire He has stirred up within her to hope for more! She than asks Him, "Are You greater than Jacob?" Are You greater than what I've know in the past?" "Are You greater than our father Jacob, who gave us the well, and drank from it himself, as well as his sons and his livestock?" Jesus had just told her that He was the gift of God that could provide 'living water' to her. She acknowledges that Jacob's gift to them had been this well. She reminds Him that it had provided water to Jacob, his family, his livestock and that Jacob's gift had been providing water to them for generations. The water that she had come to draw was Jacob's gift to his children. She is asking, "Are you greater than Jacob? Is Your gift of 'living water' truly of greater benefit?" She's is asking, "Can I hope for more?"