I don't really know. I killed her once by accident. I was a werewolf and was on a killing spree, and she got in my way by accident and i didnt realise it was her and i killed her.

what difficulty setting are you playing?

I am playing at very hard and I have an immortal tank allcharging horse , superstrong Lydia and superhuman strenght villagers ...

For God's sake Lydia now is exactly the opposite of an appropriate time to lie down!...oooooh.

I've only killed her once... sneakshot arrow riiiight to the back... and she flew about 30 feet away. reloaded game, i needed my pack mule!

I'm pretty sure she can die if the enemy she's facing is much stronger than her.

Mine got downed by a giant, and then on my other character, by the Alik'r.

And I was nowhere near her.

Like I wrote before, the guide claims that she will just get right on up if an enemy 'kills' her.

That can't be true. She's dead for good here.