Looking for a beautiful line-drawn picture book from earlier than 1975, about a witch and her daughter who live beyond the seven valleys and the seven seas. The daughter witch is selfish, and does not come home to her mother on time. Her mother sends her away until she can do a selfless favor for someone, while disguised as a regular girl. She is dropped off outside a village. Eventually, she finds a little boy who is also being punished, and helps him peel mounds and mounds of potatoes. She falls asleep doing this, and her mother comes to collect her. Ends with a line something like, "but she could never stand the sight of another potato."