Maybe because of the holiday weekend? They did a mini marathon. It was announced after episode 3 week that the next new episode would be July 12. So no worries – it’s not cancelled.
I don’t think the books ever said (maybe in book 9, but I’m still waiting for the library to get it in). I can guess, though:
Given that Eric, Bill and Pam can resist biting her, I assume it means that she doesn’t have too much “fairy-ness” to her blood despite who her real granddad was…which would also account for lemons not bothering her.
Harper’s Island didn’t air last weekend either, and both of the final two episodes air back to back tomorrow. I guess both networks decided no one would be home on a holiday weekend.