I see this problem all the time as I'm a nurse practitioner who deals with kids with stooling problems. Your daughter has had chronic constipation since she was a toddler. Doesn't matter if she goes everyday at this point (I hear this all the time). She needs a good cleanout (and preferably an x-ray verifying this). Then she needs to be on a stool softener, routine times for sitting on the toilet, high fiber diet. Her rectum is most probably stetched out from years of stool being held there. It can take 6-12 months for it to return to normal. Do a search on "encopresis"-fancy name for soiling.
My step son who is 24 now, has clogged up every toilet he has been to,grocery,department,hotels,he left no toilet un touched he drinks menamusal. he has drank that for years now, and it keeps him regular and loose enough that he dosen't clogg as many now,alot of water is helped also, his stools look like elephant poo I was amazed when he was younger that somthing that large would come out of someone so small. Try drinking some of that, they have orange flavor that is his favorite. hope this helps good luck and tell your daughter to keep her chin up,we will pray for her.
my oldest daughter has this problem dr stated to me that she needs to go everyday because when she did go they were so large she plugged every toilet even on vacation we just passed it off that was when she was smaller. make sure she is getting enough water to help regulate her bowels we used senokot just follow the dosage on the bottle we gave her the first dose the doctor said give it everyday until she feels cleaned out then cut back to half the dosage. it worked we also gave her mineral oil in juice to keep her stool soft hope this helps good luck.