The family of Annette Hewins said their mother was "let down by those who were supposed to help her."
The family were speaking after an inquest into their mother's death.
The mother-of-five became a heroin addict after being wrongly convicted of being involved in the deaths of a young family from Merthyr Tydfil in the 1990s.
In 1999, she was freed on appeal but experienced mental health problems after her conviction was quashed.
She became a heroin addict and was detained under the Mental Health Act two years ago.
She died a day after she was admitted to the Royal Glamorgan Hospital.
At the end of three day inquest the coroner ruled that Annette Hewins treatment plan at the hospital had been adequate and appropriate.
The coroner described her death as "sudden and unexpected." A post mortem showed that she had undiagnosed heart disease.
But the coroner said "it was not possible to say if the effect of being withdrawn from heroin played any part in what happened."
The inquest heard today how she had been put on four-hourly observations on the mental health ward, but that these were not always followed through and it heard that medical records of her condition while in hospital lacked detail.
In a statement the family said they hope the Cwm Taf Morgannwg health board "will act on the lessons learnt from this inquest."
Our family find it difficult to understand the lack of observations mum had in hospital and that there appeared to be no guidance on how she should be cared for.