Everyone was staring at Elena who had just killed Lilith like it was nothing, but to call her the killer was also isn't right either. They didn't actually know what had happened earlier and why suddenly Lilith disappeared without leaving a thing behind. It was like her existence had just disappeared into thin air, and all they could see was the gold mist that floated around Elena.
Elena noticed that Lilith didn't even resist and let herself be killed by her which was surprising. She realized that Lilith would prefer to die rather than get the great scheme to be revealed. The fact that Elena had to use more power to kill Lilith than the three-eyed demon gave her a picture of how powerful Lilith actually was.
Sasha already knew Elena's power, and the fact that Elena killed Lilith under Mykel's order made her realize something. Mykel was fighting the enemy that Sasha had been dealing with, and the fact that Jeanne got rid of Lucifer made her understand that Mykel wanted to help her.