I know they can be killed in HC mode, but I've already played through the game in HC mode and frankly don't want to again just for this feature.

Doubt it. I think its hard coded. Couldn't find reference to dying in her script, and by default she isnt essential. So my guess, its hard-coded.

Hard coded...haha... you are funny.

BEGIN OnCombatEND	if ( GetPlayerTeammate == 1 )		resethealth		restoreav perceptioncondition 100		restoreav endurancecondition 100		restoreav leftattackcondition 100		restoreav leftmobilitycondition 100		restoreav rightattackcondition 100		restoreav rightmobilitycondition 100	endifEND

I misread it. I thought he was asking for the companion to be able to die in modes other then hardcoe. Because unless I am running lots of high spawn mods, companions tend to mow down just about everything.

edit: So I am pretty sure I was right, even if I was answering the wrong question

Yea, he was asking if companions could be made non-essential in non-hardcoe mode.
You didn't misread it.

In non HC mode, it is hardcoded that any actor that is set as PlayerTeamMate, is essential. The 'ResetHealth' stuff in the NPC's script is just redundant - they heal after combat even without it. The function to detect if an actor has been knocked unconscious (so you can kill them with a script) is unreliable in certain cases, which is probably why you may have troubles finding a mod for this.