Some might find it bizarre that Mary refers to Saturday as the Sabbath.
No, she was not a Jew.
The controversy whether the day-off should be celebrated on Saturday (as many believed was decreed by no other than God) or Sunday (as many others believed was decreed by no other than God) became an issue in the years that followed Henry VIII’s [1491–1547] break with the Catholic Church.
When the Pope wouldn’t bend God’s Known Laws to fit Henry’s marital wishes, Henry forced the whole of England to change their religious allegiances and follow his new take on religion.
One of the changes he instituted was the keeping of the Sabbath on Saturday. It took a few centuries and many debates before England synchronised its week with the rest of the (Christian) world.