Kids.... often do this... and at this age. Even if they are/were potty trained.
It is still ongoing.
It is not finite.
BUT... the thing you want to watch out for... .is that she not get constipated.
IF a child, is on purpose 'withholding' their poop and not going... then they can get constipated.
My daughter did that. We then had to see a Pediatric Gastroenterologist, for it.
As constipation occurs, and they do not poop... it creates pain.... upon it coming out or from them withholding it.
Then, due to the pain, they do not want to go and poop.
Then, if the bowels becomes impacted internally.... it becomes harder and harder... in consistency, and then that makes it hard to come out... without pain.
Then the child, because of that, withholds pooping even more.
The Specialist we saw, says everyday he sees kids like this. He said, just let the child poop, don't force or threaten.... and even if in a diaper... let them poop. Otherwise, they get internal problems. And it can cause medical problems... one of them being "Encopresis"... which means an involuntary... leaking of poop, usually exacerbated by constipation.
Some kids bowels, if taken with an x-ray, is so blocked up and hardened... that it cannot come out... without pain. For example.
So it then becomes a (1) medical problem and (2) an emotion based problem... of the kid not wanting to poop at all, due to the pain and discomfort....
It took my daughter, THREE months, to remedy her constipation... even though we did not force her to poop. She simply got stress and anxiety about pooping.... and IN the toilet.
Try to give her things that are not binding. Pear juice helps to soften the stool.... as well as whole apple juice. Or a couple of prunes or prune juice.
The more you 'force' it.. the more the child will resist.
My son would even scream "IT'S MY BODY!!!!"
If she needs to poop... and will not in a toilet... just give her a diaper. This is per the Specialist as well. Then, as the issue lessens, then you just encourage the child again, to do toileting.
all the best,
Susan