Mrs. Weston also mimics Miss Bates, although not as amusingly as Emma does, in ch. 26:

Good soul! she was as grateful as possible, you may be sure. 'Nobody was ever so fortunate as herself!' -- but with many, many thanks, -- 'there was no occasion to trouble us, for Mr. Knightley's carriage had brought, and was to take them home again.'

I would assume that refraining from repeating a conversation with Miss Bates without sprinkling the more diverting of her expressions among it would be difficult for most light-hearted souls. One can hardly imagine saying, "Miss Bates was very grateful, indeed," and letting it drop there, as one would if Mr. Cole, or Harriet had been offered a favour.