I don't understand why the invitation hasn't been mentioned before? If she was planning on going with Chris, then she's known about it for a while, they could have mentioned it in a previous peisode briefly I would think... but hey, if she was originally planning to go with Chris, then Chris' absence is sure to be noticed maybe? We'll see...

If only she was in a place that since she "doesn't want to go alone" she could invite Luke to go with her... But, of course not...