Almost all of the recipes you see on the site are good options for kiddos as well :)
Check out these for some ideas:
As for servings per day..I'd start off with a small cup once a day and then maybe build up to to a tall one as a meal replacement (breakfast is a great time of day for a NutriBlast). At 6 you don't want to put her on a "diet" but start to make small changes towards more plant-based foods with less processed junk foods. If she is not used to eating these high fiber plant foods and then begins eating them in large amounts, this is probably what is causing the constipation. By starting off slower, her body will have time to adjust.
Check out this article about bowel regularity!
You'll read that other important parts include drinking plenty of water, exercise, stress reduction, and possibly assistance from digestive enzymes or probiotics.
Let me know if you have any additional questions. Over time, her taste buds should change. Just keep trying and be patient :)