I'm guessing the girl in the bar that Derek took an interest in was the half-sister that Meredith hadn't met yet. With her mother gone and her dad gone to pieces, I'm guessing that she's going to transfer her internship to Seattle--and she happens to be good enough to get a transfer over to Seattle Grace.

Later, to be closer to the hospital, the father may suggest/insist that she move in with Meredith? Or they get into a fight and she runs over to spend the night with Meredith? Who knows--??

Do his other daughters even *know* they have this half-sister? And where she is right now??

Derek needs to stop smiling back at women in bars--until he gets their last name first, at least!

I've never seen a show add even more characters to an already overloaded slate. The show should be two hours long every week--!