Mabel is the third "generation" in the play. While she ends up engaged to Lord Goring, she's not really in his same world (she's probably about half his age). His spontaneity is constructed; hers is natural. This may be what attracts him to her. Lady Chiltern actively fights the dunderheadedness of a Mrs. Markby, while Mabel's simply amused: "I love being scolded by her" (2.196). What she avoids is earnestness, seriousness, and any sort of purpose. She says to Lady Chiltern, "You married a man with a future, didn't you? But then Robert was a genius, and you have a noble, self-sacrificing character…I have no character at all, and Robert is the only genius I could ever bear" (2.193).
Unlike Lord Goring, Mabel never reveals a deeper understanding of the world or interest in others. Nevertheless, her last lines embody the message of the play:
An ideal husband! Oh, I don't think I should like that. It sounds like something in the next world…He can be what he chooses. All I want is to be…to be…oh! A real wife to him. (4.290-292)
In her innocence, totally unaware of the complex power struggles the others have been facing, Mabel reaches this conclusion that acceptance is the foundation of marriage. Wilde seems to be saying that's only natural, and that Mabel has come to this conclusion naturally.