30-year-old S Yamuna, wife of C Sasikumar, consumed poison and had been admitted to a private hospital, they said.
Her relatives saw her consuming the poison and falling unconscious. They rushed her to the hospital.
Hindu Munnani State Spokesperson Mookambikai Mani said Yamuna's condition was stable.
She is responding to treatment, he said.
40-year-old Sasikumar was hacked to death on September 22 here, leading to tension in the district and neighbouring Tirupur.
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Sasikumar, district spokesperson of the organisation, was returning home in Subramaniampalayam, in the outskirts, on a two-wheeler when the unidentified assailants chased him on motorcycles and attacked him with sickles.
Meanwhile, a top CB-CID official today said vital leads had already been obtained in the case and the assailants would be nabbed soon.
CB-CID ADGP Karan Singha, who is camping here since yesterday, said the investigation team of the city police had taken efforts to get leads about the killers.
"(Local) Police have done a good job, they have received vital information, which will lead us to solve the case," he told reporters here.
The documents in connection with the case had been handed over to CB-CID by the local police, he added.
Singha, who yesterday inspected the murder spot in Thudiyalur, held discussions with senior police officials, including city Police Commissioner A Amalraj about the case.