Imagine you were in her situation.
She gets stuck as a combination packmule/bodyguard for some lowlife. I'm just surprised she hasn't snapped and slit your throat one of those lomg nights when she sits there watching you.
I see your point. The Housecarl gig probably beats pushing a plow or being a grunt in the Jarl's guards. My fighting prowess probably kept her from gutting me in my sleep. However, I did not sleep much so she was probably too tired. She is in a better place now.