M.:
Miralax was NOT meant to be used EVERY day. it was a SHORT TERM solution to a problem.
Her body does NOT know how to work on its own since it has had some chemical doing it for her for 4 years.
talk with a nutritionist about your family's diet. You may think you are eating healthy but you might not be. Every one needs fiber in their diet. Apples, raspberries, banana's (yes, bananas are commonly used to help stop diarrhea too), raisins...and NUTS - almonds, peanuts, etc. are GREAT HEALTHY sources for fiber in your diet.
You say YOU walk 5 miles a day - does your daughter? Does your daughter drink enough water? What kind of exercise does SHE get every day?
There are other foods out there that help with bowel movements as well.
Do you KNOW what's in Miralax? polyethylene glycol 3350, or PEG. Try googling it and see what you are putting in your daughter's body.
This is my opinion - instead of changing her diet, you took the "easy" way out and now her body doesn't know how to work on its own. Change her diet. Change the family diet. Get EVERYONE healthy in the family and stop using "pills" or "drugs" to make it better.....
I would STRONGLY suggest you NOT use the Miralax, Metamucil - fix the problem by fixing her diet...salads, fruit, nuts, etc.
get her to sit on the toilet every day at the same time and give her a stool to put her feet up on so her legs don't go to sleep. Give her a book to read and let her sit there until she goes EVERY DAY...it may sound like torture - but you have to retrain her body to work on its own and not count on a drug to fix it.
Good luck!