Pooping probs

My 2 year old always seems to be constipated. Currently ts been 3 days since she has pooped. And i know it starts to hurt her bc when she tries to go she cries.

Dr suggested prunes and prune juice, neither of which she will eat. And she said miralax. I give her a daily regimen of miralax and it was working but now it seems to not be working anymore. She is wjth her dad 2 days a week and there is no co parenting between us so he isnt giving it to er when he has her.

Any other suggestions for what i can give her. Obviously more fiber is good but shes 2 so getting her to eat certain things isnt the easist thing in the world. And she does drink alot of water.