My DD started taking off her diaper or pull up to resist bedtime, and then would pee on her bed on purpose (she knew I'd HAVE to come back up to take care of that!) Thank goodness there wasn't ever POO involved.
BUT, what I did was cut the feet off a few of her footsie pajamas and put them on backward, She couldn't unzip them so then couldn't take off her diaper and the whole thing stopped. I no longer have to put them on backward...she's just learned to keep everything on and the novelty/control issue is over (thankfully).
Even if your LO calls for you early to change her b/c of poo...at least it will be less messy this way!
They also sell pajamas specially made to zip up in the back if you search online
HTH.