The Miralax your daughter is on is helping "clear her out". You'd be surprised how much can be back-up even though they seem to be pooping regularly.
My son went through the same thing during the potty training years (2-3). With consultation from his doctor, we tried changing his diet-more fiberous foods-to help. But, he was so afraid to poop in the potty. We were eventually refered to a specialist because not only did he have blood from tears, but blood in his stool. Come to find out, he was so constipated that polyps formed inside and when he'd try to go it irritated the polyps and they bled. My son was put on a laxative. We were told at the time that some kids (like the specialist's daughter) never come off the laxative - it's something they deal with all their lives. Not so in our case, but he was on the laxative every day for a year. At first, it seemed all my son was doing was pooping. But once the laxative cleared him out, it helped him stay regular. When the potty training issues were over, we started lowering the dosage until he was eventually off of the laxative and regulating himself.