Mathilde's life took a change for the worst after the loss of the necklace. Namely, because instead of swallowing her pride, owning to this fact and confess to her friend, she decides to take matters into her own hands. She goes out of her way to replace the lost necklace and, as a result, went in complete financial ruin.
Madame Loisel came to know the ghastly life of abject poverty. From the very first she played her part heroically. This fearful debt must be paid off. She would pay it. The servant was dismissed. They changed their flat; they took a garret under the roof.
Both, Madame and Monsieur Loisel had to give up their lifestyle to replace this piece of jewelry. Monsieur went on to invest his inheritance, and give up all this belongings. Mathilde had to take jobs and work harder than she ever had. The hard work and sacrifice reflected in her face and her daily actions.
Madame Loisel looked old now. She had become like all the other strong, hard, coarse women of poor households. Her hair was badly done, her skirts were awry, her hands were red. She spoke in a shrill voice, and the water slopped all over the floor when she scrubbed it.
The result was that she grew coarse, bitter, and overwhelmed with these things. Her beauty disappeared, and she became essentially an angry and ugly person. We know that all of this was totally unnecessary. The jewels she had borrowed were fake in the first place and there was nothing to be in need of replacement. The shock comes to the reader, and we never get to learn Mathilde's reaction as the ending comes to an abrupt stop when the truth is revealed.