Emma, once so well-groomed and refined, now went for days without putting on a dress, wore gray cotton stockings and used cheap tallow candles. (I.9.57)
Emma’s depression exhibits itself through her unusual lack of attention to her appearance.
Emma lost weight, her face became pale and gaunt. With her smooth black hair, her big eyes, her straight nose, her birdlike walk and the silence that had now become almost constant with her, did she not seem to be passing through life without touching it, bearing on her brow the mysterious mark of a sublime destiny? (II.5.40)
We can always tell how Emma feels through her appearance. Feeling separate and special, she begins to look that way, too.
The smooth folds of her dress concealed a tumultuous heart, and her modest lips told nothing of her torment. (II.5.42)
Emma doesn’t betray her passions, and is able to maintain the façade of propriety, which apparently is all that matters.
"She’s very nice, that wife of the doctor’s," [Rodolphe] was saying to himself. "Beautiful teeth, black eyes, dainty feet, and graceful as a Parisian. How the devil did she get here? How did such a clumsy oaf ever get a wife like that?" (II.7.33)
Emma’s looks are enough to make Rodolphe think she’s out of place married to Charles in a place like Yonville – we see the power of her beauty here.
[Rodolphe] was dressed with that incongruous mixture of casualness and refinement which the common people regard as evidence of an eccentric life, tumultuous passions, artistic aspirations, and always a certain contempt for social convention, which either fascinates or exasperates them. (II.8.25)
Rodolphe’s contrived appearance, a combination of wealth, eccentricity, and calculated style, immediately sets him apart from the "common people."
[…] when she saw herself in the mirror she was amazed by the way her face looked. Never before had her eyes been so big, so dark, so deep. She was transfigured by something subtle spread over her whole body. (II.9.57)
Emma’s affair with Rodolphe seems to completely possess her body, and somehow transform it.
It was for [Rodolphe] that she filed her fingernails with the meticulous care of an engraver, faithfully rubbed her skin with cold cream and scented her handkerchiefs with patchouli. She wore all sorts of bracelets, rings and necklaces. On days when she expected him to come she would fill her two big blue glass vases with roses, arrange the whole room and adorn herself as though she were a courtesan awaiting a visit from a prince. (II.12.4)
Adultery makes Emma even vainer than she usually is; her appearance becomes her main occupation.
Madame Bovary had never been so beautiful as she was now; she had that indefinable beauty which results from joy, enthusiasm, and success, and which is essentially a harmony between temperament and circumstances. She had been gradually developed by her desires, her sorrows, her sensual experience and her still-young illusions, as flowers are developed by manure, rain, wind and sun, and her entire nature was now in bloom. Her eyelids seemed to have been made expressly for those long amorous glances in which her pupils were lost in profound reverie while her heavy breathing dilated her thin nostrils and raised the fleshy corners of her lips, with their delicate shadow of dark down. Her twisted hair seemed to have been arranged by some artist skilled in corruption; it lay coiled in a heavy mass, carelessly shaped by the adulterous embraces that loosened it every day. Her voice now took on softer inflections, and so did her body, even the folds of her dress and the arch of her foot gave off a kind of subtle, penetrating emanation. (II.12.36)
Somehow, Emma’s body channels her emotions yet again; everything about her is sensuous, luxuriant, and incredibly sexy, even the fabric of her dress.
With the diversity of her moods – by turns mystic, joyous, loquacious, taciturn, passionate or nonchalant – she awakened a thousand desires in him, aroused his instincts and memories. She was the amorous heroine of all novels and plays, the vague "she" of all poetry. He saw in her shoulders the amber skin of the "Bathing Odalisque"; she had the long-waisted figure of a feudal chatelaine; she also resembled the "Pale Woman of Barcelona," but above all she was an angel! (III.5.20)
To the smitten Léon, Emma takes on the appearance of his artistic ideals; he reads his vision of the perfect woman into her.
[Léon’s] soul was carried away by her sweet words and kisses. Where had she learned that depravity, so profound and so artfully concealed that it was almost intangible? (III.5.107)
Again, we see how well Emma hides her inner state with her beautiful exterior – this juxtaposition grows more and more menacing.
She looked extraordinarily beautiful to him, and majestic as a phantom; without understanding what she wanted, he had a foreboding of something terrible. (III.8.28)
Emma’s beauty, heightened by her desperation, gives her a menacing power over Justin; again, we see her appearance impact those around her with an astonishing strength.