I'm very curious as to what EXACTLY was said. It's not that I think that Pandora is lying; not at all. But I think that for the situation she was in at the time, with her emotions and nerves likely frayed, she might have interpreted something slightly differently than they said it or meant it, or misheard, or about 100 other variations on that theme.
It is standard operating procedure to take them to a fitting room with a female manager; the fitting room is totally clean going in. They go in, take off what they are wearing underneath, then exit. The fitting room is checked again to make sure they didn't ditch any other merchandise, drug abuse instruments, weapons, etc. Then what they give back is compared to what LP knows or suspects they stole.
It's not standard operating procedure to say "open the door to show yourself," but again, I'm wondering if they didn't actually tell Pandora something like "You better make sure we know you don't still have anything on," which she interpreted as "open the door and show yourself to the manager." Also, even if they DID tell her to do this, I'm not going to venture into saying whether or not they were wrong to do so; I don't know MI law, what policies they might have gotten cleared through their district LPM, etc.
I will say that you would be shocked at how many girls I've had to literally stop from pulling down their pants, lifting their shirts, etc. in the LP office. It's almost weird how people are willing to just start undressing to prove that they don't have anything else on them. I'm not sure why they do it but I'm guessing it's just nerves along with a desire to be seen as finally coming clean.