I do not know the identity of Cassandra Alfriend, however, Elizabeth Woodlief (daughter of Peter) married Dr. Shadrach Alfriend 27 Feby 1817 in Norfolk, VA, per the newspaper announcements of their marriage.
Dr. Shadrach Alfriend appears to have died bef. 1850, as he is not in the Petersburg household of Elizabeth in 1850, 1860 or 1870. According to a gravestone in Blandford Cemetery, Petersburg, Elizabeth Blad Woodlief, "beloved wife of Dr. Shadrach Alfriend,"was born 1798 and died 1874. However, I do not know if this is an original stone or one placed in more recent years by a descendant.
If your Cassandra was born ca 1748, she precedes this Woodlief connection by quite a few years.