How does Rikki-Tikki's friend help him?

I believe the friend the question is referring to is Darzee's wife. Darzee's wife helps lure Nagaina away from her snake eggs so Rikki-tikki can sneak up to them and destroy most of the eggs.

Darzee's wife is an intelligent and brave bird. She knows Nagaina's eggs, if allowed to hatch, will produce dozens of deadly cobras. She wants those eggs destroyed, and she is willing to put herself in harm's way to help Rikki-tikki do that. Her plan is to fake an injury and lure Nagaina away. Darzee's wife flies to the ground and begins hobbling around and moaning in pain. She keeps crying out that the boy broke her wing. Nagaina can't resist the easy target, and Nagaina begins to stalk Darzee's wife. Darzee's wife continues to play up the injury while hobbling away from the cobra's nest. Rikki-tikki realizes the opportunity he is being given and seeks out Nagaina's eggs. He destroys all the eggs except one.