New York - An American aid worker who was kidnapped last year in Sudan's violent Darfur region has sued the U.S.-based humanitarian group, run by a prominent Christian preacher, that sent her there.

Flavia Wagner, held by kidnappers for more than three months before being freed last August, accused the charity Samaritan's Purse of following "a plan designed to protect its own financial and political interests by minimizing the amount of money that it would pay" for a ransom.

Samaritan's Purse, based in North Carolina, is run by well-known preacher Franklin Graham, the son of famed Christian evangelist Billy Graham.

Wagner's lawsuit, filed on Tuesday in Manhattan federal court, also accuses the charity of failing to train its security personnel adequately and of willfully ignoring warning signs that abductions were a threat to foreigners.

The lawsuit also names Clayton Consultants, a crisis-management consulting firm that was retained by Samaritan's Purse to handle negotiations with the kidnappers.

Wagner, who is 36, was released after being held by her kidnappers for 105 days last year. "We thank God that Flavia is safe and free," Franklin Graham said at the time.

Abductions of foreign aid workers and international peacekeepers have been a growing problem in Darfur since the International Criminal Court issued an arrest warrant in 2009 for Sudan's president, Omar Hassan al-Bashir, for crimes against humanity.