The identification as Durga is based on the Goddess holding chakra and shankha in her uppermost hands and the vigraha following Kerala traditions. Durga is viewed as the Mother Goddess or the Supreme Goddess. Hence the twelve arms and the range of attributes.
Durga’s front hands are in Varada (boon bestowing) and Abhaya (protection) mudra. In other hands she is holding Kalasa (water pot), Ankusha (elephant goad), arrow, a sickle (a typical Kerala one), chakra (discuss), shankha (conch shell), shield, bow, Trishul and a patra (vessel). Clockwise starting with her lower left hand. Durga is sitting in Padmasana and she is wearing a full set of ornaments. The bangles deck catches one’s attention as it seems to cover her entire arm.
Bronzes from Kerala are rarer and the subject matter, the patron deity of Kerala, makes this a special one.
As Dr Navin Kumar Marike pointed out, Durga is also known as Bhagwati in Kerala and the adjoining region. (16 May 2021).
Of special interest is the garland like decoration (or is it a snake?), above her her head and between the sickle and the shield. You see a similar feature in very early dancing Shiva vigrahas with Shiva holding a cobra with his uppermost hands. Some consider that to be a precursor to the Prabhavali.
The vigraha is about 8.4 cm in height and it is really packed with details. At some stage in its life, this vigraha was with a leading dealer in London and their site suggests this may be dated to the 15th-16th century. The age and possible ritual use does not seem to have affected the definition of the features.