That's why she has a spot in your crib. Every city will give you a carl if you complete enough quests for the Jarl, and I think they all sleep somewhere in your house, even if you're not making use of them.

Also, followers can only die by your hand, if they're kneeling and you hit them with an area effect for example. Otherwise they'll simply recuperate after a few moments.
My first Lydia is now sitting (sleeping, really) on a throne somewhere in a dungeon, for eternity. A fitting reward for going down right when I was about to use unrelenting force on the fire mage that she was fighting.