I'm sorry to say this, but... fail.
Lydia dies consistently around me. Not just "Oh, I'm on my knee because I'm hurt

" dead, but dead and sprawled out on the ground dead. Corpse. "Search Lydia" dead. Lots of reloading on my part.
She's died at the hands (claws?) of
Dragons.
Bandit Chiefs.
*regular* Bandits.
A giant (I was level 19 and it couldn't kill *me* but it laid her right the hell out).
Honestly, I'm expecting her next death to be from friggin Skeevers. Lydia is, aside from as a bipedal suitcase, completely useless to me.