*lord* = kyrios. *God* = Theos. Elizabeth did not say the mother of my Theos (God) but mother of my Kyrios (Lord)
You're making a distinction without a difference, as shown here:
In the New Testament, "Lord" is the Greek kurios, which simply means master, whether referring to God (Matthew 1:20), Jesus (Matthew 7:21), or a general authority (Matthew 18:27).