Showtime said:
Survived a massacre? Hell, she probably did it herself and has been playing the innocent victim card for how ever many years its been.
*splutters* YES.
Police arrive on scene, find however many dead girls and one live Lindsay. I know who my money's on...
Which explains her current "trauma" act. The poor schmuck she's framed for the crime is coming up to trial and she realises that there's a slim chance her carefully laid plans my fall apart if he has a decent enough defence lawyer. (Or there's a rumour of new evidence which could clear him...?) So she has to run back to Montana to do her "victim" act, to nail those final nails into his coffin. Maybe he's a dad, and that's why she can give them bad news all day.
This also totally explains why she's working as a CSI. She gets off on the violence and gore, and after killing people herself, became a CSI so she could see more of it while planning her next massacre. Getting handy tips, so to speak. Because no-one would suspect her, would they? Plus she gets to learn how to cover up her tracks...