Miralax side effects

My 2 year was in the ER on Friday complaining her stomach hurt. X-ray showed she was backed up real bad despite diarrhea since the day she was born. My daughter has never had a solid poop ever always very mushy and messy. So they put her on miralax. And it’s been 3 days she now has a rash so bad that she can hardly walk, I had to give her Motrin so she could sleep decently. I read the bottle of miralax and it says it’s only for children 17 years old up. Her dosage is HALF A DOSE of an adults. I googled it and the side effects are so so soo scary from other mother who reported irreversible effects on there toddlers. I’m freaking out alittle I know all medicine has side effects but these ones were so so scary. And the bottle says 17 and up.