When Shendu brings John Lawson back to life in the rewritten reality, the man has been (as far as Shendu's artificial memory goes) manipulated by Shendu to believe that his daughter becoming the demon's wife is best for her. The reason Shendu would bother winning Valerie's father over is that he doesn't want a repeat of what transpired nine centuries earlier; Lo Pei openly rebelled against Shendu only after the demon forcefully took his daughter Lo Mei as a bride, and after Mei committed suicide, her father turned Shendu to stone. Shendu acknowledges that the rewritten Lawson is the same valiant fighter for justice as the original one, but he'd compromise his principles when it comes to his daughter's fate. If Shendu decided to marry Valerie without her father's consent, John would certainly try to rescue her. Shendu would most likely defeat him, but if Valerie's beloved father were to be killed/hurt/imprisoned, then she wouldn't willingly offer Shendu her heart, and in the worst case scenario, she'd commit suicide like Lo Mei.
