Francois Mauriac was not a Jewish convert. You may be thinking of Jacques maritain, who was a convert but not from Judaism though his wife Raissa, was a Jewish convert. Simone Weil died through self imposed starvation as a protest but it had nothing to do with the Jews. Simone Weil remained very negative in her ideas about Judaism.
from the article: 'He'd say kaddish for his mother'