-- her remarks on the Cox sisters, whose brother Emma dismissed back in Chapter 16 as a possible husband for Harriet, though only in soliloquy, with "Oh! no, I could not endure William Cox -- a pert young lawyer." (How Harriet could endure young Mr Cox is clearly irrelevant).

So Emma wants to match Harriet with someone whom she, Emma would like to associate with -- as she used to like Mr Elton, but not consider good enough as a husband for herself.

Emma felt she could not associate with Robert Martin because he was a gentleman-farmer who rents (not owns) a farm. Could RM be considered one of the half-gentlemen?

Emma did not like young Cox, because she finds him to be "a pert young lawyer". Is he a half-gentleman -- he is a lawyer, but I suppose he was a solicitor belonging to what was known as the "junior branch" of the legal profession, and not a barrister belonging to the "senior" branch like Mr John Knightley.