Kupiec was born in Nýdek on 5 April 1920 in Cieszyn Silesia. Her Milerski family could trace their heritage to the 17th century. Three months after she was born, the region of Cieszyn Silesia where she had been born, was divided between Poland and Czechoslovakia as a result of the Spa Conference. The village of Nýdek where her family lived found itself on the Czech side of the border.