Her name is Mathilde Loisel. She grew up being very poor and unloved. But then married a rich minor civil servant at the Ministry of Education.
One day her husband came home with an invitation to the ball. But she did not want to go to it because she had to proper wardrobe or nice jewels.
So she decided to ask her rich friend Frostier to help her out. She asked if she could borrow some of her clothe and some jewels. Frostier said yes and so she decided she would go to the ball.
A little bit into the party Mathilde realized something. On pg 377 she said "It..it..its gone ". She looked down and noticed her necklace was missing. Her husband quickly realized it too and became worried.
They then accepted the fact that they were going to have to work very hard for awhile to be able to pay off the necklace. About 10 years later they decided to go to her rich friends house so they can give her the new replacement necklace they had bought.
After she told Frostier the story and apologized. But told her she had bought a new one to replace it. Frostier replied with "Oh my poor, poor Mathilde! Mine was false." on pg 390. Both her and her husband were in shock.