Kyrios is the standard Greek rendering of the divine name in the Septuagint, though it can also mean master or lord in ordinary usage.
Elizabeth's Spirit-filled recognition occurs before Jesus' birth and contributes to Luke's deliberate unveiling of Jesus' identity.
The word Lord alone is not proof of deity, but its placement within Luke 1-2 and the inspired character of Elizabeth's testimony make it strong cumulative evidence.
Elizabeth responds with Spirit-filled blessing and amazement.