In the video of Lois holding the gun that shot Sykes you can see that her finger wasn't on the trigger when the gun went off. Also blowing up the image they would be able to see there was no clip in the gun. With that evidence there is no way Lois could be charged with first degree murder unless they proved she rigged the gun to fire by itself. And even if charged with a lesser crime like manslaughter the video supported everything Lois said happened all along which would make it harder for a jury to convict her.
When Lois was released from jail the police let her know they had her under constant surveillance so they should have known that she hadn't let the house when the hallucination of her was seen downtown with the gun.