Police seized more than 13kg of cannabis and about $40,000 in cash at the end of a five month investigation dubbed Operation Foxy.
McMahon was alleged to have sold cannabis and laundered money from its proceeds between January 2005 and her arrest in June.
She pleaded guilty to the charges in September.
Wellington organised crime manager Detective Inspector Darrin Thomson said at the time that Operation Foxy had severely damaged the cannabis supply chain in the Wellington region.
"This syndicate was responsible for millions of dollars worth of drugs flowing into our community and causing damage to many."
Mr Thomson said the group had been operating for a number of years and built up millions of dollars in assets from the proceeds.
Four others were arrested as part of the operation, including McMahon's 48-year-old-son Craig McMahon.