The documentary’s director, Helena Coan, said the rough sex defence was “abhorrent”.
It was the “ultimate lie” referred to in the film’s title, she said.
“I think it is the most offensive use of the justice system.
“I think it is a very clever and manipulative way of harping on that same tune – she asked for it.”
The defence’s legal team said in court that Kempson was “just doing what [Millane] wanted him to do, or what she asked him to do”, Coan said.
“I think the fact that that’s allowed is disgusting.”
The way Millane was portrayed in court spoke to a wider issue around violence against women, Coan said.
There was still a tendency to blame the victim, rather than looking at the aspects of society that contributed to women’s murders.
She wanted to make the film in a “sensitive and compassionate way but also an honest way”, she said, and centre women’s stories.
That included the stories of other women who dated Kempson.
Coan also liaised with Gillian, through Beard, before making the film, and received her blessing.
“If she had turned around and said ‘don’t make it’ I would never have done it.”
The film will be released in cinemas on 25 April.
RNZ