nobody ever appears to criticise Emma's clothes, and I would bet any money that Mrs Elton would be offering unsolicited advice on warehouses and dressmakers if there was anything amiss with them. Mr Woodhouse indeed praises the beauty of her dress for the Cole's party. She might not be interested in Fords because she doesn't purchase much from there. I have always considered it possible that she has her fabrics and trimmings imported from London - she never visits there in the course of the book, but she may have in the past when Miss Taylor was still around to baby-sit Mr Woodhouse, and she might also entrust her sister Isabella to purchase materials on her behalf - Jane and Cassandra Austen seem to have done this for each other quite often when one of them was visiting somewhere with shops - and to send patterns to be made up locally. Isabella has good taste in dress - Emma and the narrator both describe her as elegant - so the end result would be pleasing. I don't think Emma would go for a lot of display and ornamentation in her clothes, but I don't think she would want to be dowdy either. She might perhaps feel that as she is superior to pretty well every other woman in Highbury she should look the part, and be dressed in rich but tasteful clothes whenever she appeared in public.