In the book Holes by Louis Sachar family have bad luck. Who did curse and how she do?

The character Madame Zeroni cursed the Yelnats family. Madame Zeroni is an old Gypsy who was cursed with a bad back. She says she was cursed by the witch of the mountain where her people lived. She puts the curse on those that take and have but refuse to give. She has Stanley Yelnats dig holes as a repayment.