And if I recall correctly, the son killed her and her lover for having done it (many years later).
While the scene in Brave Heart is one of the few comic moments in the film, it wasn’t true. Although it crossed Longshanks mind on more than one occasion to rid his court of the pantywaist fop. Piers Galveston died of “natural cause” in England. They cut his head off. Looks like Edward III didn’t hold a grudge against Isabella.