Quote 21
She suffered intensely, feeling herself born for every delicacy and every luxury. She suffered from the poverty of her dwelling, from the worn walls, the abraded chairs, the ugliness of the stuffs. All these things, which another woman of her caste would not even have noticed, tortured her and made her indignant. The sight of the little girl from Brittany who did her humble housework awoke in her desolated regrets and distracted dreams. (3)
Mathilde is unhappy locked up in her house, just being there makes her suffer. She finds it oppressive. Her only method of coping with it is to live in a dream world. The question is, does Mathilde just suffer because she's excessively greedy? Or does she suffer because her life is boring and meaningless?
Quote 22
And she wept all day long, from chagrin, from regret, from despair, and from distress. (6)
In case you needed any additional proof that Mathilde is miserable, she spends all day crying. Her life has essentially nothing enjoyable in it.
Quote 23
She danced with delight, with passion, intoxicated with pleasure, thinking of nothing, in the triumph of her beauty, in the glory of her success, in a sort of cloud of happiness made up of all these tributes, of all the admirations, of all these awakened desires, of this victory so complete and so sweet to a woman's heart. (54)
This represents Mathilde's one moment of genuine joy. It's just about the only such moment in the whole story, and forms a high point between two long bouts of unhappiness.
Quote 24
And he went out. She stayed there, in her ball dress, without strength to go to bed, overwhelmed, on a chair, without a fire, without a thought. (79)
The object which made Mathilde's glorious night possible has become her worst nightmare just a few hours later. She's so traumatized she can't even get out of her chair. How quickly the situation reverses. The fact that Mathilde's hasn't even changed out of her lovely ball gown captures that reversal in an image.