Perhaps she was able to assimilate the crime. Or at least she thought that and she only suppressed her memories. Until she was confronted with the trial and the murderer. I could imagine that being a CSI means to her that she would never become a victim again and she would be never helpless. Mac sending her back to lab- she could have had the feeling of failing to be able to handle with the situation. But I agree that it would have been better if Lindsay had been the one asking to go back to lab. It would have been more understandable. Not being able to cope with the crime in season 3, it could result from the fact that she was faced with the trial. That could be something like a second victimization, having to remember the crime, to tell everything again. She could have felt like being transported back to her youth. Oh God, I don´t want to know how wrong I`m with that. But that was just my feeling when watching season 2 and 3.