The Wikitree profile shows that she was the daughter of King Richard I, the Lion-Hearted, and his wife. Charles Cawley's Medieval Lands Index does not show the Richard had any legitimate children. (Other sites show that son Phillip was legitimate.) I can find no source for a daughter, Isabel.
Also, Isabel is not shown as a wife of William de Burgh. The identity of his wife is uncertain. That font of wisdom, Wikipedia says: "A book of genealogies recorded in the 15th century by Cú Choigcríche Ó Cléirigh, one of the Four Masters (published in Annalecta Hibernica 18), indicates that the mother of Richard Mor de Burgh, William's son and successor, was the "daughter of the Saxon [English] king", an illegitimate daughter of Henry II of England or perhaps Richard I of England."
I say, cut off her head!
Before you "cut off her head" though, I would suggest you contact the profile manager and see what they say about the matter...
Click on Profile manager: Lindsay Coleman Lindsey Coleman or Stough-48 ( http://www.wikitree.com/wiki/Stough-48 ).
Very interesting discussion!!