A cry for help - with a shitty parenting dilemma

I'm at a loss. I really don't know how to deal with this stage of potty training.

My other 3 kids did not go through this - I can't remember how they started poo'ing on the toilet, but they definitely didn't go through this. I would have remembered.

Aisha (2) has been lying on the bed, crying for the past few hours. She no longer wants to poo in her nappy - nor is she ready to do it on the toilet.

So she just keeps it in. And cries and cries - with pain and discomfort.

Her record thus far is four days. That means four days of discomfort with bouts of pain (because it comes and goes). But it amounts to four days of misery.

Then, when it happens, she transforms into a different child; a happier, more normal child.

I feel helpless. I can force her to eat. I can force her to dress. But how do I force her to poo?

I thought about giving her prune juice for its laxative effect, but the problem is not that she can't go - it's that she doesn't want to. Perhaps I should give it to her anyway, to increase the urge to go, so that she cannot fight it for as long a period.

We've made an appointment at the doctor. I don't know what good that will do, but I suppose it can't hurt to hear if she has any suggestions - I, myself, am all out of ideas.

Any suggestions?