Jane Fairfax is seen as competition to Emma and displays the same sorts of qualities, which Emma demonstrates to the reader. Despite the fact that she is socially inferior to her, Emma still finds her to be competition. We can therefore concur that Jane Fairfax puts maximum effort into trying her best to escape the social restraints of her current low social standings. She has successfully done this accordingly due to the fact that she is engaged to Frank Churchill. But as you can see, the only way in which she is similar to Harriet is that because both are socially in a low position they have to marry someone like Frank Churchill/ Mr. Knightley to achieve stable social standings. .
We can therefore concur that social destiny for Jane Fairfax has always stayed the same, she had to marry someone with high standings in order to escape her low life working as a governess, so Austen gives us what would actually happen to a lady with low social standings in the character portrayed by Jane Fairfax. We do though see a difference in Harriet's destiny, as it takes a different turn.
Harriet Smith is the daughter of an unknown rich man who is not a resident of Highbury. Portrayed by Austen to be pretty and sweet-tempered, she is a student in the boarding school run by Mrs. Goddard in Highbury. She looks up to Emma with awe for her wealth, social status, and intelligence. Because Harriet is pretty and sweet-tempered, Emma feels certain that she can mold her into a suitable wife for a gentleman of the landed gentry or upper class. She foolishly convinces Harriet that Robert Martin, a perfect match for her, is socially beneath her. In his place, she involves Harriet with Elton, who has no interest in this plain, poor girl. When Elton rejects Harriet, Emma pushes her towards Frank Churchill. Ironically, it is really Knightley to whom Harriet is attracted. Her involvement with him is the spurring factor that causes Emma to analyze her own feelings for Knightley.