Oh, I rather left out that part of the story. Part of the way through the six years, a young king discovers the princess in the woods--where she's been living alone, sewing the shirts from the thistles--and takes her back to his castle with him. And he likes her very much, but his mother doesn't trust her because she refuses to talk. So the mother ends up paying some women in the town to say that their babies have been killed, and makes it seem as though the princess is responsible. The princess can't speak to defend herself, so the law forces the young king to sentence her to death by burning at the stake.

Luckily, the date of her execution is also the day the six years comes to an end, so as she's tied to the stake, her brothers come swooping down and she throws the shirts over them, and they change back into humans again. And then she can speak to defend herself, and does, and they end up burning the prince's mother at the stake instead. And then the princess and the king get married and live happily ever after.