L.M.
Kimberly gave you a lot of great advice. I will add a few things from my holistic practice.
This is fixable, despite what some other poster's Dr. said. Most Dr.'s are not required to take more than 10 hrs. of nutrition in med school anyway.
In addition to fiber, water is extremely important in this equation. Smoothies are a great way to get veggies, and fiber into her. You can disguise many veggies in a smoothie. Get to Whole Foods or MOM's and look for the non dairy smoothies. Dairy is definitely a big issue. Look at labels because even cheeses that say soy, or almond sometimes have casein( dairy product) in them.
There is a wonderful chiropractor in Annapolis that works on children. I don't have the name near me. But feel free to contact me and I can get this to you.
Chiropractic can help with potty issues.
Keep working on it.
L.