So Elizabeth is declaring her fealty to a fetus?
A foetus who was God incanate.
Don't forget Elizabeth had already declared her fealty to God.
She was, along with Zecharia, "righteous before God, walking in all the commandments and ordinances of the Lord blameless." (Lk 1:6). And when she spoke she had been "filled with the Holy Spirit" at the sound of Mary's greeting. Even the child in Elizabeth's womb "leaped in her womb".