I ran past a haunted house and some skeletons tried to kill us so I ran. It gave me the message "Neeshka has fallen behind" and then it brought her closer except she was down and almost dead. I'm using realistic fatigue so I could hear her panting and she wouldn't get up. I was able to get her up by either knocking her unconscious or going away and using the summon spell. When I save the game it crashes and it becomes a corrupt save. I also would get the double face follower bug when waiting for her to get up after making her unconscious. I know that was because I moved a mod in the load order but I don't know if that has anything to do with the save becoming corrupt. If I can't fix this then I have to deactivate the mod.

I also used the friendship ring for companion detection mod on her. Maybe I wasn't supposed to use that on her?

A 'general solution' that is always worth trying when a companion (or any npc) acts up is to leave him/her behind for +72 gamehours.

I.e. go somewhere else, to a cell where Neeshka isn't present, rest for +72 game hours. Return to her. Chances are good that she is normal again.

However, if her behaviour is because of a conflict with another mod, it might not help, and it is of course not a workable way to fix an already corrupt save.