There were others, however, who felt that the voice had benefitted from the weight loss. Of her performance of "Norma" in Chicago in 1954, Claudia Cassidy wrote that "there is a slight unsteadiness in some of the sustained upper notes, but to me her voice is more beautiful in color, more even through the range, than it used to be". And at her performance of the same opera in London in 1957 (her first performance at Covent Garden after the weight loss), critics again felt her voice had changed for the better, that it had now supposedly become a more precise instrument, with a new focus. Many of her most critically acclaimed appearances are from 1954–58 ("Norma", "La traviata", "Sonnambula" and "Lucia" of 1955, "Anna Bolena" of 1957, "Medea" of 1958, among others).