Emily Titterington had not been to the toilet for three months when she suffered a cardiac arrest at home.
An inquest heard the condition was so bad that some body parts had been displaced, including her diaphragm.
The Coroner for Cornwall concluded the cause of death was "natural causes contributed by psycho-social factors".
Summing up, Dr Emma Carlyon said it could have been prevented.
"Something went wrong with the patient-parent-professional triangle which meant she did not get the care she needed," she said.
Paramedics described their "shock" at Emily's "grossly extended abdomen" when she collapsed at St Austell in February 2013 and said she was "vomiting faeces".
The inquest was told that Emily, who was home-educated, had a history of constipation that could be linked to her anxiety and mild autism.
Her sister Hannah Herbert raised concerns about the impact "parental anxieties" had on her, and said she had warned social services "something terrible might happen" the year before.
Her brother-in-law Brian Herbert told the inquest Emily's decision not to be examined or go to hospital would have been influenced by the fact her parents "could not cope" with that.
However Emily's GP, Dr Alistair James, said her mother Geraldine Titterington had tried to persuade her to be examined and he found no evidence of safeguarding issues.
Consultant paediatrician Dr Paul Davis said "self-neglect" played a part in her death but she should have been persuaded to go to hospital.
A serious case review by Cornwall Council's Safeguarding Children Board has made several recommendations including that agencies share concerns raised by a family member.
Dr Carlyon said she was satisfied "most of the recommendations have been actioned and embedded".
A 16-year-old died from chronic constipation because either she, or she and her parents, resisted the care she needed, a coroner has said.