R.
I can totally relate! My 4 year old (at the time he was not quite 4) didn't go for 4 weeks this summer. I think he was just too afraid to go or something. I took him to the pediatrician when it had been almost 3 weeks. She gave me a prescription for polyethilene glycol to give him every night in his juice for a week. It works by keeping water in the stool and not letting it absorb back into the bowel. After a week, still no joy. I called the doc again and she said to try milk of magnesia. Well, about 2 days later he had a humongous BM and I think it hurt so much that now (almost 6 months later)we are still having issues with him sitting on the toilet to go.
Is she truly constipated or is she willfully holding it in? Either way it is not good. Ask your pediatrician if there is something to give her to soften her stool. Good luck