A woman who supplied heroin to people while working for an organisation that helps drug users has been jailed for more than two years.

Rosemary Rebecca Kaniski, 68, pleaded guilty last year to 26 counts of offering to sell or supply a drug to another.

The Perth District Court was told the charges related to very small quantities of heroin.

Kaniski was employed by the West Australian Substance Users Association (WASUA), which aims to help people with drug problems by encouraging safe use of substances.

She had been employed by the organisation since 2007 and had been a volunteer before then.

Three other former employees are also facing charges after an investigation by WA Police that involved the interception of mobile phone calls over a three-week period.

Ms Kaniski had used a mobile phone supplied by WASUA to facilitate the drug deals.

Defence lawyer Justine Fisher told the court the people who purchased the heroin from Ms Kaniski were not clients of the association.

Ms Fisher said Kaniski was a dealer and user who had been struggling with substance abuse since the age of 17.

She said her client benefited from the transactions by being supplied with small amounts of heroin for her own use, but did not make a financial profit.

Judge John Staude said Kaniski had previous drug convictions including a four-year jail sentence, suggesting she understood the consequences of her offending.

"Ms Kaniski, sadly, has a 50-year heroin addiction," he said.

"It's a very sad story.

"But clearly you are not a first offender and cannot claim leniency on that basis."

Judge Staude also made observations about the way the Government funded WASUA operated, saying drug users supplying other drug users with syringes under the guise of being non-judgemental undermined the prohibition of illegal substances.

Kaniski will have to serve 13-and-a-half months before she is eligible for parole.