According to news reports, Cecilia Sarkozy flew to Tripoli on Sunday to help prepare the nurses' return to their home countries.
She is accompanied by Claude Gueant, the secretary general at the French Presidential Palace, and Benita Ferrero-Waldner, the European Union's externalrelations commissioner.
News reports say Mrs. Sarkozy met with the daughter of Libyan leader Moammar Gadhafi on Monday. Nicolas Sarkozy also spoke to the president of the European Commission, Manuel Barrosso, several times overnight by phone.
French secretary of state in charge of parliamentary relations, Roger Karoutchi, said Mrs. Sarkozy has no power to negotiate but is in Libya as an intermediary.
But after her first visit to Libya, Mr. Gueant, the president's secretary general, said that her visit was meant to send a strong message to the Libyan government.
He told the French radio station TF1 that since no one is closer to Nicolas Sarkozy than Cecilia Sarkozy, her presence underlined the French government's concern over the future of the six prisoners.
Bulgaria's foreign minister said he expected negotiations to free the nurses would end sometime on Monday. It's expected that they would then be flown to Sofia aboard Mrs. Sarkozy's plane.
The government in Bulgaria wants them to be allowed to return home. It has granted citizenship to the Palestinian doctor so that he may also benefit from any deal to transfer the nurses to Bulgaria.
The six, who say torture was used to extract their confessions, have been imprisoned in Libya since 1999, accused of deliberately spreading HIV in a childrens' hospital.
Foreign experts say the infections started before the nurses arrived at the hospital, and are more likely to have been a result of poor hygiene.
The French news agency, AFP, quoted sources saying that in return for the nurses' freedom, Mr. Sarkozy has promised to modernize the Benghazi hospital wherethe infected children were staying.