The woman's testimony stems from 20-year-old allegations against Stephen Huggett, who was charged in August 2013 with invitation to sexual touching and sexual interference with a child under 14 years.
Police say she was introduced to the accused through her mother, who was an aquaintance of Huggett's.
She says the molestation lasted for about six years.
Taking the stand at the first day of the trial before a judge alone, the complainant said she was scared to come forward and talk about what was happening to her.
Huggett, 61, who has pleaded not guilty, spent nine months in jail in 2009 for possession of child pornography.
He retired from the Calgary police service in 2007 after 25 years with the force.