My potty-trained 2 y/o will only poop in her sleep, anything I can do to ease this problem for her?

Ever since she's started making solid poops, she often pooped in her sleep. Now that she's potty trained, she ONLY poops in her sleep. She complains before her naps about needing to poop, but won't do it either in the potty or her underwear. She just tortures herself until she's asleep and her body lets it go then. I'm sure she's asleep while she's pooping, I've seen it. I put her in pull-ups for naps, but when she wakes up she's mortified by the poop in her pants. Poor girl, what can I do?