The Demons [1973]

As the scarlet flames lick her pale and desperate face while the feeble body is eager to succumb, a vindictive unrepentant witch doomed by the Grand Inquisitor Jeffries and Lady de Winter to die at the stake vomits her last malignant and sulphurous curse to all those guilty of her ordeal. As a result, petrified and with the curse of demise upon the accusers' heads, Lord and Lady de Winter set out to trace the witch's dark bloodline, and in particular, her daughters Kathleen and Margaret who have been raised as Sisters in the Blackmoor convent since childhood. But within the nunnery's thick stone walls, rabid desire and evil possession govern, furthermore, only one daughter is the curse's true heir. Which one is granted the power of retribution?