K.L.
Very, very common, and completely normal. It is just part of the process for some kids. My ods was completely pee trained for 10 months, wore underwear, but would ask for a pull-up to poop. I didn't worry about it as I would rather deal with a dirty pull-up then poopy pants! Eventually, I started having him help me flush the contents and waving goodbye to them. The next step I tried was to have him stand in the bathroom to poop-hard for you since she is hiding it but if you can talk to her about it calmly and explain that it's okay for her to use a pull-up but that she needs to ask you to put it on and then she must go into the bathroom, because that is where we poop. We don't poop in the living room, etc. Once my son was pooping in his pull-up in the bathroom, I made a chart with a prize for him to earn once completed. He was to poop in the potty 5 times then he could earn it. It took a little while but he finally did it. Once he did it once, I think he just caught on quick and never had another pull-up.
Don't sweat it. It will pass however you go about it.