is what's in Emma's head as we see from two circumstantial pieces of evidence - Jane from drowning and perhaps dying (LOL) and Harriet from those horrible gypsies who might have kidnapped her, done physical harm in trying to grab her hat or coat or money or chain. :-D

I think Mr Knightley danced with Harriet to make up for her rejection by Elton and to make her feel good. IMO he wasn't doing it to show people that they should treat Harriet well and not neglect her.
I give more credit to people's thinking.

I'm not one of those who think Emma's or Elton's behaviour is going to bring any change in people's attitude towars Miss Bates or Harriet.
CH:1 Miss Bates is loved for herself.

"It was her own universal good-will and contented temper which worked such wonders."

No, Emma would never speak to her father that way.
We all tend to love our parents more. Very normal IMO.

In all fairness to Emma she does see the value of Miss Bates;
CH:10
"she is only too good natured and too silly to suit me; but, in general, she is very much to the taste of everybody, though single and though poor. Poverty certainly has not contracted her mind: I really believe, if she had only a shilling in the world, she would be very likely to give away sixpence of it; and nobody is afraid of her: that is a great charm."

It's her letter reading and chatter that tests her patience, and that is what she said at Box Hill, about her talking.

Mr Knightley agrees to Emma's devalued opinion of Miss Bates.
CH:43
To Emma's;
...but you must allow, that what is good and what is ridiculous are most unfortunately blended in her."

He answers;
"They are blended," said he, "I acknowledge; and, were she prosperous, I could allow much for the occasional prevalence of the ridiculous over the good.

It's just that Emma shouldn't have said it.
It's **this one time** she slipped so I'm not going to dwell too much on this especially after the fact that she has shed tears over the matter and repented.