I implied that Emma never had any gowns, or had none stitched. She 'must' need to wear clothes. :)

Hannah stitching clothes for Emma is just what's in my mind too.
Simple, practical gowns. Doubt if Hannah is a fashionable seamstress. A situation identical to Harriet's getting hers stitched by some other needlewoman.

I'm just looking at information that we get from the book till now.
It must mean something when we get to read about 'Harriet and gowns', from the narrator, but nothing about Emma's interest in them, or gowns in Emma's thoughts - about which we are given so much detail. For instance *thinking* about what she would wear for the Coles' party*

>I think Mr Knightley is referring to Emma's not being vain about her face and figure and bloom of good health in Chapter 5

He says;
Considering how very handsome she is, she appears to be little occupied with it;

I take this to mean that her 'little occupation' with her handsomeness involves clothes which are part of being handsome. Mr Knightley doesn't have to be a fashion expert to know when a woman is very occupied with it, in her manner of talking and interests.

>if Emma's clothes were visibly out of date Mrs Elton - who certainly would keep up with the latest fashions - would have had some unwanted advice to offer her,

I doubt she would do that openly even if she thought her unfashionable due to 'open respect';
CH:33

the enmity which they dared not shew in open disrespect to her,

If they feel they have to show respect I'm sure she wouldn't come up with unwanted advice to Emma the way she comes up with it for Mrs Goddard, Mrs Coles etc

Since we are hardly given information about other people's thoughts, who knows what Mrs Elton thinks of Emma's dress sense in private.
We do know what the Eltons think generally though.

There was no reason to suppose Mr. Elton thought at all differently from his wife.[....]

"having brought such a woman to Highbury, as not even Miss Woodhouse could equal;"

"When they had nothing else to say, it must be always easy to begin abusing Miss Woodhouse; "