Hi My Daughter Has Constipation.i Noticed Her Constipation When She

Hi my daughter has constipation.i noticed her constipation when she started cow milk and solid around age of 14 months.she use to drink 4-5 cups of milk and was not eating much. Her constipation was increasing but was able to solve with prun juice.
At her age of 2 we noticed she is having Iron deficiency. We treated her for 3-4 months with polyvisol and her ferritin reached 13 from 5.
But her constipation is still going on.
We recently found stool impaction in 2-3 places in her colon and also again ferretin came 9.
I again started iron with 2-3 doses and with that in 3 months it reached up to 15. We did her enimas also.
But constipation still going on. We went to GI specialist and she gave her Miralax that is poly glycol. Osmotic laxative and she told to continue it for months.
My question is her pediatrician is suspacting hirshsprung ,is this possible?we did her stool test but it was fine also.