8 yr old has probs with constipation, it made her sick & had heartburn. now breathing fast, started when she was very backed up. dr or will it go away?

Depends: sometimes kids can breathe quickly with either the pain of constipation or from abdominal competition, where the distended belly doesn't allow the lungs to fully expand. However, if she is having a hard time catching her breath or the rapid breathing is severe or persistent, she should definitely be evaluated by a dr.

Chronic constipation: in childhood can stretch & eventually weaken spots in the the walls of her intestines. See her pediatrician for her acute pain & referral to a pediatric gastroenterologist for a "clean-out" of her bowels, then daily Miralax (polyethylene glycol) for at least 6 mos. at a dose that yields soft stools ar least every other day + sitting on toilet for 15 min., 15 min. after dinner nightly for "bowel retraining."