Mary's last name, in terms of her Irish heritage and dark skin, does raise an ethnographic eyebrow.
September 13, 1759
The Pennsylvania Gazette
RUN away the 4th of this inst. September, from John Galbreath, of the City of Philadelphia, a Servant Woman, named Mary Brown, she is of a swarthy  Complexion, and has sorish  Eyes;
had on when she went away, a brown and white cross barred Worsted Gown, a spotted Gause Cap, and a blue Ribbon,  a brown homespun Shift, a Linsey Petticoat, and half worn Shoes and Stockings.
Whoever takes up and secures said Servant, so that she may be had again, shall have Forty Shillings Reward, and reasonable Charges, paid by JOHN GALBREATH.
N.B. Said Servant came over from Ireland with Capt. Dingee, about this Time last Year.
1. A dark tone of skin, late 16th cent.: alteration of obsolete swarty (see swart).
2. I am unable to find a definition of sorish. If this is a misspelling of sourish, it could mean squinting, as if having eaten something sour.
3. That this runaway girl in an alien land, having spent a year in circumstances in which it is almost inconceivable that she was not raped, should wear a blue ribbon on her gause [thin, as is gossamer] cap is touching.