Police allege Jolly Shaju, 47, admitted poisoning her first husband, his parents, her current husband's ex-wife and two others between 2002 and 2014.
Her youngest alleged victim was just an infant when she died in 2014.
Mrs Shaju was remanded in custody until 16 October with two other suspects accused of being her accomplices.
One of them, Prajikumar, a goldsmith accused of supplying the cyanide, said he was innocent of all charges, according to the Press Trust of India (PTI). He said he had thought she was buying it to poison rats.