Gretka tells Ciri the story of how she came to be in the forest all alone. Apparently, her family was unable to feed her and sent her to 'follow the trail of treats' which would lead her to a well-known orphanage in the forest. Gretka got lost chasing a butterfly while following the trail and thus ended up in the predicament Ciri found her in.
Ciri watches over the girl until after their meeting with Phillip Strenger, the Bloody Baron. She requests that the baron keep her as a cooking wench in his castle. Gretka can be found inside the kitchen of the Baron's castle at Crow's Perch after completing the King of the Wolves quest.