for clarifying that.

Emma certainly has preconceived ideas.
She thinks Harriet on a chance meeting will accept the proposal which Robert would make again.

She thinks a man in love wouldn't/shouldn't go to dinner when his love is unable to.

I'm pretty sure Emma has these preconceived notions from some book. I wonder which. Some gothic novel, which also gives her the idea Harriet is higher class.

The other part of my comment was with regards to Emma honouring Harriet's wishes which is in 'earnest'. This was telling IMO.
I meant that to support my interpretation that Harriet 'can' be earnest when she has these earnest feelings, and Emma honours them. She might try to influence, but I feel against Harriet's earnestness her conscience would prevent.
After all she doesn't use drastic measures as seen when she tells Harriet only afterwards that she wouldn't have been able to be friends with her if she had married Robert Martin.