Hi My Little Girl Is 2 And A Half And

Hi my little girl is 2 and a half and is currently taking movicol. Its seems to me that her constipation is more psychological? Is it ok to give her milk of magnesia? Or can you suggest something else, she is terrifed to pass stool. Her belly becomes rock hard and she is constantly getting cramps but sits on thr floor to hold it in?

Thank you

Serena