"Why does she not do her job?"

Translation: Perché non fa il suo mestiere?

[eisalehi]

In English there is a significant difference between having a job (lavoro) and having a trade (mestiere). Are the Italian terms really interchangeable?

[f.formica]

Mestiere was originally used to refer to those activities that were learnt by practice rather than study, and usually accosted to arts in that category (arti e mestieri); the broader meaning, more common nowadays, refers to the set of practices that make up a job, its know-how. So a retired plumber doesn't have a job (lavoro), but it's still a plumber (mestiere).