If her sister is okay with being inside a tent, I would make a really long "dust" ruffle to go on the upper bunk. I would take off the upper mattres, and attach some stone patterned fabric all around to a plain flat sheet cut the size of the mattress. The stone fabric would need to have a seam in the bottom center for access to the lower bunk. If that much stone fabric is out of your price range, I would buy gray flat sheets and make a stone template to trace and make stones on it with a permanent marker. As for putting anything around her ladder, no that will be a safety risk.