Do you mean the evidence before Jayme was found? If so, I would say it was to preserve some evidence for the killer to substantiate as evidence. And Jayme, too.
After she was found. I think that is to protect her story. As far as her smiling, who knows? She may have been responding to a cue from the photographer... maybe she is so happy to be with her aunts and cousins.
I kind of think the pictures *may* have been taken through the windows by over zealous reporters, and I get what you are saying those items may have been relics from when JP’s sister lived there.