The celebrated "red coat girl" from Schindler's List, Polish actor Oliwia Dabrowska, has revealed she was left traumatised after breaking a promise to director Steven Spielberg not to watch the film until she was 18.

Dabrowska, aged three when she filmed a key role in Spielberg's landmark 1993 Holocaust drama, adapted from Thomas Keneally's novel, said she was "horrified" when she watched the film when she was 11. "It was too horrible. I could not understand much, but I was sure that I didn't want to watch ever again in my life." She also said she "really regretted" not paying attention to the director's suggestion that she "grow up into the film", and not watch it until she was older.

"I was ashamed of being in the movie and really angry with my mother and father when they told anyone about my part," she said. But, having revisited the film as an 18-year-old, she said she realised "I had been part of something I could be proud of".

The "red coat girl" – a rare spot of colour in an almost entirely monochrome film – is glimpsed in the film during the scenes of the liquidation of the Kraków ghetto, walking through the city streets as German soldiers enact atrocities against the civilian population, and then later among a pile of bodies on a cart.

• This article was amended on 4 March 2013. The headline was changed from "filming" to "watching" and the standfirst also changed to reflect this.

• This article was amended on 5 March 2013. The word adult was changed to 11-year-old in the standfirst.