Problem with a 6 mo old puppy, she was crate trained and now she soils her crate at night?

I got my 2 puppies in late Jan.(they are papillions) I had them both crate trained ( same crate) they were 16 wks old when I got them. by 20 weeks they were both staying in crate all night without soiling.(from 10:00pm to 6:00am)the last 2 weeks my female is pooping at night. I've put her in her own crate small enought to stand in but not soil in back and lay in front, this hasn't helped she will poop then lay in it. I've tried geting up at 4:00, 4:30 ,5:00 and can't catch her I've even tried puting her in her crate an hour later. Ive pulled food up earlyer. These guys are taken out right before they go to bed. I have ran out of ideas. I have even called my vet he thanks it's a behavior problem. please help any ideas will be tried. she will be 6 mo 4/4/.Genie