I'm beginning to think the entire thing may be a Dimere setup, including the room in the castle, the exploding filing cabinet, and the hidden, encrypted files that Billie copied onto the CD. It seems like the writing is pointing in the direction of the whole thing being a plot to break up Bope.
I think Chelsea is Georgia. Even the actress who plays her has dark hair and eyes, which would be a given considering both Billie and Bo have dark hair and eyes. Also, I do beleive it's a plan to break them up, but remember Tony said he had been planning for years so I beleive this is all part of his sick twisted plan.
She seems to be very manipulative. It appears that she is purposefully trying to corrupt Abigail. Is there a reason for this? It seems that this ties into Jack being held prison again, and the way someone is trying to break J/J apart.
So, that makes me wonder if she is also playing a part. She seems older than her supposed years. Maybe someone hired her to get at Abigail, and more specifically to play the part of Georgia Brady to break up Bo and Hope.
I like the idea that Chelsa is Georgia and after Billie and Bo find out who she is she beings to brainwash Billie and use her to obstract ISA information for whoever has hired her.