Her mother was the daughter of Joseph Simon, a preeminent Jewish merchant of Lancaster, while her father, whose surname originally was Grätz, immigrated to America in 1752 from Langendorf, in German-speaking Silesia.

[2] Michael, who was descended from a long line of respected rabbis, and Miriam were observant Jews and active members of Philadelphia's first synagogue, Mikveh Israel.

Gratz is said to have been the model of Rebecca, the daughter of the Jewish merchant Isaac of York, who is the heroine in the novel Ivanhoe by Sir Walter Scott.

[5][6] The claim has been disputed, but it has also been well sustained in an article entitled "The Original of Rebecca in Ivanhoe", which appeared in The Century Magazine, 1882, pp. 679–682.

Among the marriage offers she received was one from a Gentile whom she loved but ultimately chose not to marry on account of her faith.