According to reports reaching in Chennai, Nalini had sought to be shifted to a jail here so that she could oversee the work relating to her daughter Harithra's wedding.
Harithra is living in the UK and plans to visit Chennai for her wedding.
Nalini's application for parole was rejected by the prison authorities.
She began her hunger protest on Thursday. The jail officials were not available for comments.
Nalini was sentenced to death by a special court for her involvement in Mr Gandhi's assassination at Sriperumbudur near Chennai on May 21, 1991.
The sentence was commuted to life imprisonment after Sonia Gandhi, the former Prime Minister's wife, petitioned for clemency -- for the sake of Nalini's daughter.
Nalini, an Indian, had accompanied the Sri Lankan woman suicide bomber who blew up Rajiv Gandhi with concealed explosives.
Nalini, who was a close friend of an LTTE operative known as Murugan, another accused in the case, later gave birth to the girl in prison.