Sarah Reed, an inmate at Holloway prison in north London, took her own life on 11 January 2016.
An inquest jury has now found that delays in her psychiatric treatment and failures in care contributed to her death.
Deborah Coles, Director of INQUEST said, “Sarah Reed was a woman in torment, imprisoned for the sake of two medical assessments to confirm what was resoundingly clear, that she needed specialist care not prison.
“Her death was a result of multi-agency failures to protect a woman in crisis. Instead of providing her with adequate support, the prison treated her mental ill health as a discipline, control and containment issue.
“Serious mental health problems are endemic in women’s prisons, with deaths last year at an all-time high. They continue because of the failure of the governments to act.
“The state’s responsibility for the deaths like Sarah’s goes beyond the prison walls and extends to failure to invest in specialist mental health services for women and provide alternatives to custody.
"More deaths will occur until we stop criminalising people in mental health crisis and invest in specialist community services for women.”
Last year there were 22 deaths in women’s prisons in England and Wales.
The inquest into Sarah Reed's death raised huge questions about the state of the prison system in Britain.
Sarah was left in a dirty cell for days on end, with a screen in front of the door blocking the hatch.
Since the death of her child in 2003 Sarah had been diagnosed with various mental illnesses.
Despite Sarah's history of mental illness and worsening condition, prison staff reduced the frequency of their check-ups on her.
Zita Holbourne, Sarah Reed Campaign trade union liaison officer and chair of Black Activists Rising Against Cuts UK said that "the gross injustices Sarah experienced, leading to her unexpected death have been of great concern to the trade union movement. The evidence heard at the inquest leaves more questions unanswered. Sarah's family deserves to know the truth."
Sarah Reed had been assaulted by police officer James Kiddie in November 2012. Kiddie was convicted of common assault in March 2014 and sentenced to a community order.
In a statement read out by the coroner at the opening of the inquest, Sarah Reed’s mother, Marylin Reed, paid tribute to her daughter. “Sarah was adored and loved by the whole of her family. She was very much treasured. Her death has been devastating for us.”