Susanna was likely born about 1635. She was a married woman when she died, but does not appear to have had any children. Her husband died just a month before she did. His will gives a few clues to family relationships:
6 FEB 1663 - James Billingsly, planter of Calvert Co., calls Walter Carr his brother & gives him the choice of one of my best cows. His brother Thomas Billingsly all his best cattle. Cousins in Rappahanock whose names cannot be put in writing one cow whenever they demand. His wife, Susanna, was executor. 
Susanna Ewen Billingsley left a very complete will that gives a lot of information about her family relationships.
Abstract of Will
Susanna Billingsly of Anne Arundel Co.
27 DEC 1663
To my brother Richard Ewen the tobacco which he has in hand.
To my brother John Ewen sheep
To my brother-in-law Thomas Billingsly the head of cattle which I have below at the Clifts considering that he pay three calves to his cousins at Accomack which was left them by my husband James Billingsly.
To Walter Carr a cow which is at the Clifts already left him by my husband and all that my executors may satisfy Walter Carr for what he has done for me.
To my sister Ann Ewen my feather bed and all the furniture, all the pewter, and two cows.
To my sister Elizabeth Talbott the cow at my father-in-law’s Capt. Burgess.
To my sister Suffia two cows and flock bed and all that belongs to it.
To my sister Susannah Burgess a calf
To Edward Parrish a cow calf left him by my husband’s will.
Witnessed by John Cumber the younger, and John Gray present at the writing. Probate 9 FEB 1663/4.
6 APR 1664 John Ewen was granted administration on the estate of Susan, relict of James Billingsley. Bond was put up by Capt. William Burges.