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.
Not turning over the phone makes me wonder if there were phone calls or text messages that for some reason Beth is trying to conceal. She may think she has a good reason for hiding it, and she may think it doesn't have anything to add to the investigation, but I still think the investigators should have everything.
And not turning over the camera makes me wonder the same thing. Maybe it pictures from the late nights and early mornings hanging out at Carlos and Charlies, but there could be stuff in the background that helps the investigation.