A man with schizophrenia and psychosis stabbed his niece to death "in a frenzied attack" and then killed himself, an inquest heard.
Lisa Butler, 48, and Richard Thompson, 66, were found dead in his caravan in Mansfield in August last year.
The inquest in Nottingham heard Mr Thompson had been "severely mentally ill" in the months leading up to the killings.
A coroner said Mrs Butler had "just been trying to help her uncle".
The court heard Mr Thompson had been admitted to hospital just before Christmas 2017 following a suicide attempt.
He was diagnosed with late onset schizophrenia, schizophrenia-like psychosis and light mental impairment but was deemed well enough to live in a caravan in Tall Trees Park Homes in Forest Town after being discharged three months later.
On 28 August Mrs Butler went to Mr Thompson's home to take him grocery shopping, as she did every week.
When she failed to return home, her daughter and her daughter's boyfriend went to the caravan park and found Mr Thompson and Mrs Butler's bodies on the floor with a knife between them.
Coroner Mairin Casey concluded Mrs Butler had been unlawfully killed, while Mr Thompson died by his own hand, with stab wounds to his neck.
The inquest was told three months prior to the killings, Mrs Butler told a health team Mr Thompson had stopped taking his medication but there was no evidence a psychiatrist had briefed them about the potential consequences.
The coroner said there were "failures in care, missed opportunities and serious learning lessons" but admitted that even with the best care, it may still have happened.
Describing Mrs Butler's death as a "tragedy", she added: "It is my sincere hope that lessons will be learned."