Ela não revogou. Ela certamente tentou o seu melhor, mas parece que uma vez que você deu a alguém um presente mágico , revogá-lo é impossível (ou pelo menos requer mais magia do que Malévola é capaz de reunir).
A novelização oficial do filme nos dá boas informações sobre o que está acontecendo.
Feeling dread begin to build in the pit of her stomach, Maleficent spoke the words again, with still more passion. And then she repeated them. Again, and again, and again she spoke, mustering all her strength and willing all her magic to break the curse. The room began to shake as the massive amount of magic collected in the small space, but Maleficent went on, oblivious. All she could see was Aurora, sleeping the way she would forever if the curse could not be broken. Letting out one last cry, she threw her staff in the air and sent a huge burst of magic raining down over the room.
But it still didn’t touch Aurora.
Lowering her staff, Maleficent slowly left the room, her heart aching. She had done everything she could. Yet the curse, the one she had so foolishly called a gift, could not be undone. Which meant, one way or another, in a few short weeks, Aurora would prick her finger on a spinning wheel and never wake up.