A woman accused of murdering her partner allegedly told a prisoner she'd slit his throat during sex and “it was the best orgasm she ever had”, a trial has heard.

The woman, who can only be referred to as LR, is charged with murdering the man despite his body never being found. He was last seen in their Reservoir home in Melbourne’s north May 2005.

LR has pleaded not guilty to murder, and the 45-year-old disputes any involvement in her partner’s disappearance.

A prisoner, whose identity is also protected, told the Supreme Court she became close friends with LR when they met on remand.

LR gave her presents, such as chocolates, and cards - including a pink Minnie Mouse one- in which she wrote about their special friendship.