The daughter of the woman, identified as Arunaben Savaliya, who was also made to consume the substance, is in a critical condition.
A police official said a domestic dispute seems to be the cause behind the suicide by Savaliya.
As per police, Savaliya made her son Lakshya and daughter Rashi consume poison at their home in Piyava village in Visavadar taluka, around 320 kms from here.
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While Lakshya died on the spot, Savaliya and Rashi were rushed to Visavadar referral hospital, a local police station official said, adding that the woman died during treatment. Rashi is battling for her life, he said.
"The woman consumed poison along with her son and daughter, apparently after a domestic dispute. However, the exact trigger behind the extreme step is not known," the police official said, adding that further investigation is on.