UPDATE: Kudos with Amy for coming back at me. I have written her a personal note to let her know that I AM A SINGLE MOTHER with a son who is 18 now, so I KNOW it is hard. I wrote to Amy to explain why I wrote WHAT I wrote....
You say: "At nap times and when I get her up in the morning, she is always naked and has either pooped or at least peed in her crib" Well, then, it is simple. Set an alarm for youself or something and YOU go in and wake her up before she wakes herself up, and guess what? No more coming in to find her naked! and then YOU can take her to the potty to go pee or poop. AND you say she will not keep clothes or diaper on. Well, you must stop doing anything but KEEPING YOUR EYE ON YOUR DAUGHTER. Let things go for a few days in the hosue. It seems to me that you are a stay-at-home Mom, so don't turn your back on her, then she can't undress herself. If you are watching her, as soon as you see her start to attempt to undress, you stop her. It really is that simple. She will continue to undress if you don't watch her or if she wakes herself up, so it's your choice, I guess, if you want her to stop. OR, try what someone else said: DUCT TAPE.