Very, very gently do I think that by claiming she didn't get a good look at Cooper, what Tina is really saying is that she doesn't want to deal with it any more. From what I'm remembering she also readily went along with whatever the FBI agent interviewing her said at any given time. I would imagine that's probably not too uncommon a reaction for crime victims to have, and the FBI would compensate by relying on the input from other witnesses.