Directly after " The course of true love never did run smooth;" Lysander continues: "But, either it was different in blood,--

HERMIA O cross! too high to be enthrall'd to low.

LYSANDER Or else misgraffed in respect of years,--

HERMIA O spite! too old to be engaged to young.

LYSANDER Or else it stood upon the choice of friends,--

HERMIA O hell! to choose love by another's eyes."

At the moment, Harriet appears to be Hermia, and Emma, Egeus (when they are not Io and Brieze!)
This should make Mr Elton, Demetrius (and indeed, he is said to be a worthy gentleman) but Mr Elton's behavior reminds me most strongly of Nick Bottom, the (not noticeably) humble weaver, as he appears and receives his part, enquiring if he is to be: " a lover, or a tyrant?

QUINCE A lover, that kills himself most gallant for love.

BOTTOM That will ask some tears in the true performing of it: if I do it, let the audience look to their eyes; I will move storms, I will condole in some measure. To the rest: yet my chief humour is for a tyrant"

At the moment, I cannot see Emma as a Helena. Although she might be a Puck, or the Faerie Queene, refusing to surrender her page in spite of what Mr Knightely says.