How do I explain Mrs. Elton's character in Jane Austen's Emma in terms of irony that amuses rather than disgusts?
The reason Mrs. Elton amuses rather than disgusts or irritates, for that matter, is precisely because of Jane Austen's ironical approach to drawing her character in Emma. This is well illustrated in Chapter 32 where we first get a good look at Mrs Elton. Austen writes Mrs. Elton's dialogue with great gusto--words fly at a rapid pace through long phrases; Mrs. Elton will not suffer to be read in a slow manner as she fills in extraneous details and flits from one subject to another, all with the purest (misguided) sense of charm and appeal imaginable, never entertaining the wild thought that only she could possibly be interested in her brother and sister's modes of transport:
My brother and sister have promised us a visit in the spring, or summer at farthest ... and that will be our time for exploring. While they are with us, we shall explore a great deal, I dare say. They will have their barouche-landau, of course, which holds four perfectly; and therefore, without saying any thing of our carriage, we should be able to explore the different beauties extremely well. They would hardly come in their chaise, I think, at that season of the year. Indeed, when the time draws on, I shall decidedly recommend their bringing the barouche-landau;
Another good example of how irony keeps Mrs.Elton from disgusting us is her scene with Mr. Knightly in Chapter 42 in which she boarders on offending the reader but is quickly brought back from the precipice of disgust by Austen's mastery of craftsmanship and skill; by witty irony; and by Austen's exquisitely precise characterization. Knightly has just proposed the famous strawberry picking excursion and Mrs. Elton has just informed him that it is she who will invite the guest for the excursion to his home--a suggestion that rightly does not sit well with Knightly. Mrs. Elton's pushy approach is interrupted with Austen's ironical tone first by Mrs. Elton's mortification at the thought that Knightly would allow any other woman to orchestrate his guest list ("Mrs. Weston, I suppose," interrupted Mrs. Elton, rather mortified."). She is saved a second time from disgusting by Austen's next ironical rescue in which Mrs. Elton acquiesces to Knightly, then resumes her silliness by giving him commands on minutia to orchestrate how the day will go:
… but as you like. It is to be a morning scheme, you know, Knightley; quite a simple thing. I shall wear a large bonnet, and bring one of my little baskets hanging on my arm. Here, -- probably this basket with pink ribbon. Nothing can be more simple, you see. And Jane will have such another. There is to be no form or parade -- a sort of gipsy party. We are to walk about your gardens, and gather the strawberries ourselves, and sit under trees; ....
So, Austen saves Mrs.Elton from being disgusting by (1) employing an ironical tone; (2) characterizing Mrs. Elton as innocently vain instead of arrogantly vain; (3) making her a very silly person who has a doubtable grasp on logical order of thought; (4) giving her a quick and lively personality, albeit a silly one; and by (5) giving her some redeeming qualities, like her devotion to her husband and to Jane Fairfax: “I shall bring Jane with me -- Jane and her aunt.”