It was famous enough that it was made into a TV movie over there, I believe — my mother just recently tracked down a copy of it for me that we’re going to be watching together soon! Agnieszka is a little girl who goes into an enchanted forest to rescue her lost cow and ends up breaking the curse that divides her village from the one on the other side. I always loved as a child hearing a story with a little girl as the hero. The story is about not fearing and hating foreigners, a story that I have to think was inspired by the war and upheaval of the time: the magic phrase is “the people on the other side of the forest are just like us.”
Here’s a picture of the book on the official website for her (and her husband, a famous poet himself): http://www.kigalczynski.pl/natalia/prace/ — the little girl in the blue dress is the little girl Agnieszka from the story, that’s the edition I have.