Answer:
Nagaina, Nag's mate, readily joins her husband in terrorizing the garden. She conspires with Nag not only to ambush Rikki-Tikki—striking at him while Nag distracts him—but also to murder Teddy and his family in order to get rid of the mongoose and regain control of the garden.
Nagaina wanted to get rid of Rikki-tikki because he was a threat to her family.
Nag and Nagaina were the cobras that lived in Rikki-tikki’s family garden. Nagaina tried to attack Rikki-tikki at several points during the story, because she knew that he was a great danger to her...