Too much fiber blocks me up to the point I have to take laxatives and I have IBS with chronic diarrhea.
It's too bad you didn't listen to the doc...Miralax is wonderful and it's not anything like what you're describing here. Go back to the doc and get another prescription and get the other kind. Use it like YOUR DOC says.
Most of the time I listen to the pharmacist in all things but this one? He might have been trying to help but he gave you a different med/changed the prescription than the doc said and that's crossing a line in my opinion.
Put the Miralax in a small size pitcher of Koolaid, half the amount Koolaid makes, then keep it in the fridge out of her reach. Label it on top so no one else mistakes it for general drinking. The kids come in and grab the Koolaid after school and chug a glass down. It's cold, it tastes good, and they want more but I give it to them out of the pitcher of regular Koolaid.