Daphne was probably his favorite scooby-doo character. I believe one of his friends was going as Daphne as well? I hate when parents dictate what they dress up for Halloween anyway... that should be their choice, it helps them be creative. So with him being a fan of Scooby and the friend dressing up as Daphne as well, I think he just wanted to do something with his friend. I know for this halloween the brats all went as animals.. three of them were bears. A cat. A skunk. People asked me why they were all dressed as animals and I told them that's what they wanted to be. Nothing big like this story, but heh... I did say I hated when parents dictated the small things like that.
Anyway, I like the mother's acceptance and open mind.