[1][2][3] Ferrand was born in Alès, the daughter of a classics teacher, and went to secondary school in Nîmes.
In 1939 she and Roger Apéry placed first in the mathematics agrégation; she began teaching at a girls' school in Sèvres, while continuing to do mathematics research under the supervision of Arnaud Denjoy, publishing three papers in 1941 and defending a doctoral thesis in 1942.
[4][5][6] In 1943 she won the Girbal-Baral Prize of the French Academy of Sciences, and obtained a faculty position at the University of Bordeaux.
[4] One of her accomplishments, in 1971, was to prove the compactness of the group of conformal mappings of a non-spherical compact Riemannian manifold, resolving a conjecture of André Lichnerowicz, and on the basis of this work she became an invited speaker at the 1974 International Congress of Mathematicians in Vancouver.
[4][7] She married mathematician Pierre Lelong in 1947, taking his surname alongside hers in her subsequent publications[5] until their separation in 1977.