Kind of a gross subject here but I am so frustrated and I was hoping maybe some one on here is having the same problem or someone they know has a child that stool holds.

My dd she is 3 1/2 yo and she started potty training at 2 1/2 and she did fine peeing no problem there. So goes pee by herelf now in the potty without any help from me. The problem is pooping! She totally holds it and its not just for a little while I mean for a week or longer! She will get to day 3 or 4 of holding and look bloated and her mood will change she also will not want to go out anywhere because she is uncomfortable. It is a battle with her and she is totally winning. There is no taking her to the toilet and making her sit on it to go poop she will not and I feel this is discouraging to her because I am trying to control something she wants too. She is not constipated because when she does go it is soft so I know that is not an issue. I have tried Miralax and I will not go that route again because it was miserable for her and its not a natural way for her. I would rather go more for a natural way for this. I am doing as much fiber as I can in her diet. She is the worlds more pickest eater so her diet is not the best. I just don't know what to do any more I never thought I would have to fight my child to poop. I am afraid she will get use to enemas and suppositorys because after she reaches the week mark that is what I have to do. Just in case you are wonder I have taken her to the doctor for this and they are the ones that recommended Miralax for her. Any suggestions here?
Thanks