In 1995, Gardiner completed the Avalon Film and TV production course, and went on to work with producer
Larry Parr at Kahukura Productions. She began producing short films, and also co-produced a 26-part series
Lovebites. In 2009 Gardiner wrote and directed
Mokopuna, a short film about a part-Māori girl who struggles to embrace her roots; the film won the best short film award at the Canadian indigenous film festival Dreamspeakers. In 2017, Gardiner joined a team of women directors and writers to create the feature film
Waru, which focuses on child abuse in New Zealand. In 2021, Gardiner and Briar Grace Smith co-developed and co-directed the feature film
Cousins, an adaptation of the 1992 novel of the same name written by
Patricia Grace. With its release, Gardiner and Grace Smith made history as the only Māori women to have directed a feature film since the release of
Mauri by
Merata Mita in 1988. In 2023, Gardiner worked as an executive producer on the feature film
Red, White & Brass, a Comedy Drama inspired by a true story of a Tongan super fan's attempt to get tickets to the Tonga vs. France Rugby World Cup. ==Honours and awards==