She must defeat Mordred her half brother and his book of beasts .
Merlin and the Book of Beasts ( 2009 ) Laura Harris plays the daughter of Guenevere and Arthur .
Guenevere must defeat Mordred Guenevere 's half brother and Arthur 's book of beasts .
Merlin and the Book of Beasts ( 2009 ) Laura Harris plays the daughter of Guenevere and Arthur .