First thing that struck me whilst reading this thread was both Georgiana's and Anne's companions are styled Mrs. To me that could mean either they were widows or the Mrs. was a curtesy title, similar to the idea that all cooks were styled Mrs. even if they weren't during a later period. Just a thought.

As Ramya said Mrs. Jenkinson could have been Anne's Governess who got "promoted" to companion when Anne got too old for a Governess. I have a feeling (or I am just guessing) that Mrs. J. was a poor relation of Lady C's and it "suited" Lady C to keep Mrs. J "on the payroll". I imagine Lady C was often out and about sorting out the neighbourhood and can't count on Anne's health enough to have Anne accompany her as "second in command".

In the eyes of the world (even) Lady C. can galavant(spelling?) without meeting censure for neglecting her sickly daughter because Mrs. J. is keeping Anne company.

As to the "duties" of a companion as far as P&P is concerned I see Mrs J. keeping Anne company(when Lady C. is out and about) maybe reading, chatting, playing the piano and maybe, just maybe, moaning about Lady C. etc.

Em, moaning about Lady C.? As if we would.