You can try several things:
Cherries - fresh from the produce section (although I have NO idea if they are in season right now.)
*Apple juice, white grape juice, prune juice
Pears, Apples, Prunes (try the "SunSweet Ones, California Prunes" brand -- my daughter loves them!), Raisins
Dairy products can be constipating, so limit her milk intake until she is "normal" again. Also, if she's eating cheese, stop that if you can.
*Also, WATER -- have her drink more water. Put the Benefiber in the water instead of the milk.
You might also check with your pediatrician about a possible stool softener for her. If she's had poops that hurt, she may be holding it in because she doesn't want to hurt again. The stool softener will help it to not hurt and hopefully, she won't hold it in -- because that makes constipation even worse.
Just try a few of these things -- you don't want her to end up with the opposite problem!! The main thing is to get more liquids in her, so definitely give her MORE WATER and try one of the juices I mentioned.
And, reinforcing her going to the bathroom (with poops) might help. A good time to have her go is right after eating. Try having her sit there for about 10 minutes -- maybe read her a story to keep her there. She might have an easier time of pooping if she can rest her feet on a step stool. Anyway, if she poops, give her lots of praise to positively reinforce the behavior.
Let me know what ends up working for you! Good luck!