Ms na Nagara said the source of the methadone, which was not prescribed to Mrs Rink, could not be identified. She was satisfied, however, that the overdose was not deliberate.
In her ruling she noted Barnett Henderson, a close friend of Mrs Rink, had visited her at 10pm the night before she was found dead in her bed.
Her husband and son went to bed before Mr Henderson left the house early on August 28.
Mrs Rink would drive Mr Henderson to Bulls to collect his methadone three times a week. A witness said he had seen Mr Henderson inject Mrs Rink with methadone after they had collected it.
The coroner's report noted "Mr Henderson flatly denies having given Mrs Rink methadone and flatly denies having administered it to her. He was aware she used methadone but stated she had her own sources."
Mr Henderson had later suggested Mrs Rink may have stolen his methadone.
Ms na Nagara said the conclusion to be drawn from those comments "is that he was looking to explain the means by which Mrs Rink got the methadone and to divert suspicion that he had willingly provided it to her".
"I do not find his assertion compelling, as if he believed Mrs Rink had been stealing his methadone for some time, I would have expected that he would raise the concern at the time, and not just after her death." But, the coroner said, "be that as it may, this does not mean Mr Henderson supplied the methadone that killed Mrs Rink".
She said although the evidence and circumstances pointed towards Mr Henderson as supplying the drug, the evidence was not compelling and fell "significantly short of the threshhold required for finding in that regard".
The coroner's court heard that Mrs Rink had suffered from "poorly controlled" diabetes most of her life. Although she did not drink in the years before her death, she "regularly smoked cannabis, on average one or two tinnies a week".
She had been unwell on the night of August 27 and would not eat dinner. After Mr Henderson arrived, he persuaded her to eat something and ensured there was enough chopped firewood in the house. Mr Henderson had lived with the Rink family for five years but had moved out in the year before Mrs Rink died.
The second post-mortem examination found a level of 0.3mg of methadone per litre of blood, a level associated with methadone-related fatalities, particularly with people who didn't use the drug regularly.
