HERE is a REALLY FREAKY theory.
What if this was pre-planned, but the plan went wrong.
I.E. Brenda/Damon had planned to have Danielle kidnapped for a few days or so, and INDUCTED into the GIRL'S CLUB?
Later, the abductors would let her go somewhere around the hood, and someone would 'find' Danielle alive and well, and everyone would be HAPPY. DW would have been off the hook (he was just to keep police busy).
But something went wrong, and Danielle ended up dead.