Mathilde loses her beauty and looks old after she pays back the price of the real necklace.
Before borrowing the necklace, Mathilde was not wealthy, but she had beauty. However, she wanted to be rich. After she borrowed and lost the necklace and had to pay back the loan, she lost what little wealth she had and her beauty.
Madame Loisel was a beautiful woman. On the night of the ball, with her dress and the borrowed necklace (even though it was fake), she was the hit of the evening.
Madame Loisel was a great success. She was prettier than any other woman present, elegant, graceful, smiling and wild with joy. All the men looked at her, asked her name, sought to be introduced.
After she loses the necklace, everything changes. First of all, they do not know that it is fake. They borrowed it from her rich friend, and they think it is a real necklace. They borrow money to buy a real diamond and return a real diamond in its place, and then they have to work that off for years.
The time and hard work are not friendly to Madame Loisel. Before the incident they were comfortable. Her husband was a clerk, so they were basically middle class. Madame Loisel is sent into the downward spiral of the “horrible existence of the needy” for ten whole years.
Madame Loisel looked old now. She had become the woman of impoverished households--strong and hard and rough. With frowsy hair, skirts askew and red hands, she talked loud while washing the floor with great swishes of water.
The stress and hard work make her look like this. She dismisses her servant, has to do housework, and has to stress about paying off the debt for a decade. That can do a lot to a person. Then she learns that the necklace was a "paste." How ironic.
The lesson here is that you should always tell the truth, I suppose. Of course, the true lesson is that you should not want more than you have. Mathilde should have appreciated what she did have, which was her beauty and the love of her husband, instead of coveting a position in society.