She looks exactly like Agiri, the only exception being her eyes are black and somewhat squinted, however she is unable to close them fully like Agiri can.
Yasuna sees her and tells Sonya about it. Sonya immediately knows, she is a fake. But Fake Agiri persists and wants to show them a ninja trick with a crystal ball to prove it. While Sonya and Yasuna are distracted, she attacks them from behind with a bat. She hits Yasuna instead of Sonya however and then reveals her real identity as an assassin.
The real Agiri then comes in and notes that she is a doppelganger of hers. Agiri makes herself look even more like the fake Agiri, so the trick works better. The Fake is proud to say, they can't tell them apart anymore and wants to make a double attack. She gets beat up by Sonya and Yasuna. She is shocked, that the real Agiri didn't help her. She then takes the bat and slams herself unconscious with it.