What happens to Mathilde in “The Necklace”?

Mathilde borrows a necklace from a friend of hers that is better off than she is, then she loses the necklace. Rather than admit that she's lost it, she and her husband purchase another one and it costs them everything they have (including their health). Later, she finds out from her friend (when she finally does confess to losing the necklace) that the necklace was not worth anything to begin with.