S.S.
I read what everyone said and it's so true. The key here is two fold. One is the need to change the food she eats to include a lot of water based fruits and not too much fiber. Too much fiber can be drying and hard to move.
In the beginning it's about teaching her to trust her body again. You want to begin with stool softeners and tell her she has to get out the stuff that's in front of the soft stuff. Tell her she needs to be willing to go as soon as she feels something so she can get the hard poop out, so the soft poop can begin.
This is going to sound silly but a child will feel empowered by it. Have her talk to her body. Have her talk to her poop and cheer her self on. This makes her feel like she plays a part in this and isn't just being taken over by pain.
Use the stool softener for about 2-3 weeks. The anus is the only muscle in the body with a mind of it's own. It will close off even when you don't want it too, especially if there's been lots of pushing and pain. So both the anus and the child have to be retrained with softer stools. Good luck, this is not fun.
S.-www.proactiveparenting dot net