I take what Beth says with a grain of salt. I think she wouldn't have a problem exagerrating something or denying something else if she thought it would help implicate those she wants to see convicted--sort of like an over-zealous prosecutor. It is good in some ways, but it also blinds her to other possibilities.
I've heard that she refuses to hand over Natalee's cell phone and she refuses to hand over her camera to investigators. That is very odd in my opinion.
Given the performance, or lack thereof, of the ALE, why would you find it odd that Beth would not want to hand over her daughter's belongings? I imagine that girl's room hasn't been touched, either.
I still think she knows things that have not been made public. It would serve no purpose, nor give closure, for her to want to see and assist in convicting the wrong person. I'm sure she knows that. She's done a pretty good job of living this nightmare - I hardly think she is anywhere close to caving.