Antonia Coello Novello (b. 1944) was Surgeon General of the U.S.
1990-1993, the first woman and also first Hispanic to hold that
position. No opera singers by that name that I can find, but maybe
you are thinking of Clara Novello (1818-1908)? (Coello=Clara?) She
was the daughter of the London music publishing magnate Vincent
Novello, and sang in premieres of sacred works by Mendelssohn and
Rossini; considered one of the three best English sopranos of her
day.