Omission of Jane Fairfax in the movie

Comparing the novel Emma and its movie adaptation a striking difference is noticeable. Although most characters are maintained in the adaptation Jane Fairfax is left out. Jane Fairfax is a woman about the age of Emma, who passed most of her life in the company of Colonel Campbell (a friend of her father’s), his wife and his daughter. Colonel Campbell is described as a respectable man who decided to take care of the little girl after the death of her parents. Janes nearest of kin were her grandmother and her aunt, both of them lived a humble life and hardly had a sufficient income. Her aunt Miss Bates was a very popular and always welcomed person, although she was “neither young, handsome, rich nor married” (cf. Emma p.22). She cares for her mother, Jane’s grandmother, the widow of a former vicar of Highbury and together they live in a small and simple home.
Mr. Campbell provided her with a good education with the intention of her becoming a governess in the future, for the money she inherited from her father was not enough to secure her financial independence. In the end, however, she marries Mr. Churchill, the son of Mr. Weston and consequently does not have to seize the ultimate measure (cf. Emma p.373) of engaging herself as a governess.
The question that arouses at this point is: What would have been the motive for the author of Clueless to leave this character out? On this question one can only theorize. In the following some