“So she uses Lord to mean Jesus and then uses the same exact word a sentence later to mean something different entirely....God.”
No, she means master or Messiah. Not God.
Blessed is she who has believed that the Lord would fulfill his promises to her!”
This refers to God fulfilling his promises, not the Messiah. So, no, when she said Lord, she meant Lord.
"....the mother of my Lord (God)."