Through the Valley of Shadows - S1-E2
Audio problem: After they discover the rogue planet that they can mine oxygen from, Niko tells Javier and Bernie to inspect the outside of the ship for damage. When the camera cuts to them, you can hear Javier respond in full with a sentence as the camera is focused on both of them, however their mouths aren't moving at all.
Answer: First, it should be pointed out that Ian didn't actually attack Niko. He had a knife, made a vague threat about not being as magnanimous as she was to him, and did raise the knife after approaching her, but she kicked him first. But the crew had already mutinied against her. The way I see if, she wanted to make sure the crew thinks she was willing to kill anyone who was a threat to the mission. Whereas if she claimed self defense she would either look weak or a look like a liar.
Bishop73
The crew members that followed Ian might not believe he would try to attack for no reason. She had no marks on her, so if she claimed he attacked her first, she would be lying. Most of the crew that was awake already mistrusted her, so claiming self defense at that moment wouldn't make them start trusting her.
Bishop73