Inara is a member of the highly respected Companion community. In their most absic sense (i.e. in Mal's slightly immature mind), Companions are prostitutes. However, it is not that simple. They can be likened to the Geishas of Japan: they are trained in many arts, and sex is only one weapon in their arsenal. They are highly respected (except, of course by Mal, but then he probably has a huge crush on Inara).
Inara's seemingly fragile beauty is misleading: she knows how to hide a weapon whilest wearing very little, and she knows how to use it.
Inara: (rearranges guns) "Every well-bred petty crook knows -- the small concealable weapons always go to the far left of the place setting."