LOS ANGELES—About two years ago, employees who managed Walt Disney Co. ’s princess characters gathered to watch an extended scene from an unreleased movie.

The executives had spent years cultivating Ariel, Elsa and Snow White as highly profitable models of femininity. The footage they saw, from this month’s animated feature “Ralph Breaks the Internet,” revealed the princesses as everyday young women, on break from their jobs as Disney royalty.

Elsa and Sleeping Beauty have their hair down and wear pajamas. Snow White shows off her Coke-bottle glasses. Cinderella shatters her glass slipper and thrusts it forward like a broken bottle at a girl who walks into the room. Rapunzel asks her, “Do people assume all your problems get solved because a big, strong man showed up?”

“Everyone audibly gasped,” according to a person present. In their eyes, the scene broke all of the Disney rules that had built the princesses into a lucrative brand.

For nearly 20 years, Disney employees have debated how far the company should go in updating its heroines for the modern age. The crux: How do you keep princesses relevant without alienating fans who hold fast to the versions they grew up with? Billions of dollars of revenue—dolls, sequels, stage shows and dresses—hang on getting that balance right.