Penny has been found, I am so relieved! That is exactly where she was - inside our box spring and apparently could not find the hole she got in through to get back out!!! She must have remembered how she used to get in son's bed after we first got her and went to hide there when our friend got here. I even pulled all the underbed boxes out and shined a flashlight around up under there earlier and didn't see her. i don't know how she hid that well.