Daughter of the Forest

Daughter of the Forest is a fantasy novel by Juliet Marillier first published in 1999 It is based on "The Six Swans" (a story that has many versions, one of which is by the Brothers Grimm). A girl must sew six shirts from a painful plant in order to save her brothers from a witch's curse. She must not speak until the task is finished.
Plot summary.
Sorcha, the seventh child of Irish Lord Colum of Sevenwaters, has been raised by her six older brothers. Having lost her mother at birth, Sorcha is almost ignored by her father. Her father's new wife, the Lady Oonagh, attacks Sorcha and her brothers. Sorcha alone is able to flee into the forest and escape. Sorcha's brothers, however, have been turned into swans.
The story is a twist on the classic tale of "The Six Swans." Sorcha learns that if she can spin six shirts from a painful plant she can free her brothers from the spell. But she must not speak until the last one has been finished. Sorcha agrees to this and spends several years in the forest hiding as she works on the shirts.
After several years of hard work, Sorcha is saved from drowning by a British lord, Hugh of Harrowfield (known as "Red"). When Red returns to Britain, Sorcha accompanies him. Red believes that Sorcha knows something about his brother, Simon. Sorcha had nursed Simon back to health after his capture by Lord Colum. Sorcha stays with Red as she works on the shirts.
While in Britain, Sorcha finds a new danger in the form of Lord Richard, Red's uncle. Sorcha must fend off the attacks of Richard as she works to save her brothers.