The film is "Wildfire: The Legend of The Cherokee Ghost Horse" ... director Eric Parkinson tells TMZ he's adding an "In Memoriam" as the movie's final shot, right before the final credits.

Eric tells us Anne was superb in the movie, which started filming back in 2019 before being delayed by the pandemic, and the entire cast and crew are devastated by her death.

Anne plays a rodeo trainer in the film, and Eric says during negotiations to hire her for the role, her agent cautioned she was not an experienced rider, so producers decided they needed a stunt double for some barrel racing scenes.

The plan for those riding scenes, we're told, was for Anne to slowly ride up on the horse and then cut to the stunt double ... but once they were on location in Oklahoma, Anne surprised everyone.

We're told Anne politely asked the stunt double to get off the horse, then climbed in the saddle and told Eric to roll ... and that's when she took off on the horse in a full gallop, executing the barrel turn and racing to the finish in record time.

Shocked, Eric says he went up to Anne and told her what her agent said about her not being an experienced rider ... to which Anne responded, "I'm not ... but my character is a champ!"