Dyddgu was the daughter of Thomas ap Llewelyn but her mother is unknown. The date and place of her birth have not been found.
Her husband was Gruffydd Goch ap Gwilym. They were married, but the date and place have not been found. Their two known children were Ieuan ap Gruffudd (?-?) and Efa verch Gruffudd Goch (?-?).