Brad, maybe the pronounciation of Deye as "Day" might be Baltimorese! Die makes more sense and in the old records, I've found it spelled "Dye" which made me think that it was pronounced Die.
Penelope Deye was indeed the literal mistress of Taylor's Hall as she and Thomas Cockey never married. At his death he was the 3rd richest man in Maryland and although he did not go so far as to legitimize his children with P. Deye, he did leave her and them everything. The widow Cockey sued and won (though she died before the suit ended and their daughter inherited her mother's widow's share of Thos. Cockey's estate). As part of the condition of being mistress of Taylor's Hall, Thos. Cockey stipulated in his will that Penelope Deye remain single -- which she did.
Brad, I'm interested in hearing more about the Twaites heritage of P. Deye.