A home enema, like a suppository, isn't going to clean her out well, and it's not going to reach the upper part of her digestive tract. So I can see that she might need more than that, but if the in-hospital and at-home procedures are the same, then hospitalization makes little sense, even without the NG tube which I agree would be traumatic.
I think you need another opinion, big time. You don't trust the doctor and you feel forced into things - yet you have a 7 year old with a persistent problem. She might be "holding it in" (and I've seen that in my nephew and my stepdaughter) but it shouldn't affect the entire digestive tract over and over. A colleague's child had problems with a kink in his intestine, but that was picked up on x-ray and ultrasound, showing impacted feces. So you should be demanding tests that show where the blockage is.
I'm sure you know that these endless enemas aren't solving the problem. So I think you should, in the absence of an emergency in your child, cancel Tuesday's hospitalization and get another pediatric GI appointment ASAP. You're in a major city, so I'd call the nearest children's hospital and get the first available appointment with a team - psychologist, GI specialist, social worker and behavioral expert. You could also consider talking to the manager/head pharmacist at your local pharmacy to see if any of the products used for colonoscopy prep are safe for children. Make sure that what you're using orally and rectally are compatible with each other too. I work in food science and have worked extensively with people (all ages) with chronic constipation and there is a lot you can do with food-based products that will bypass a child's desire to hold it in without a battle.