the end. This shows that Maupassant is not attacking nor criticizing Mathilde's poor system of values, but showing her overall ignorance and dissatisfaction with life. Therefore, it is evident that Maupassant rather uses Mathilde to illustrate the little prospects women had in the 19th century when they lacked money, whether they were attractive, or intelligent, worth marrying, or not. The author's message may be summarized in one simple statement: Life offers much but some are meant to get little. Society may not be fair, but sadly, it is what it is.

Notice that Mathilde obviously lacks more than just money.

She would so much have liked to please, to be envied, to be seductive and sought after

She wants attention, perhaps romance, and intellectual challenges. Her wedding was planned, as it often happened during that time period and, as previously stated,  she had little prospects. Mathilde grew up without enough exposure to sophisticated persons, places, or things. Case in point, the fact that, out of all the beautiful jewels she could have chosen from, she gravitated toward the most extravagant-looking, yet, less valuable piece.

Moreover, Mathilde's husband is a pretty dull man, which is a trait that is not necessarily mitigated by being kind. Who likes dull people around them, especially when one has no choice about it? Mathilde is literally helpless to change her life. As a result, the woman can only complaint about her situation, while not really knowing what else to do about it.

...she cried all day long, from chagrin, from regret, from despair, and from distress

Not all of these are reflections of a woman-gone-bad. These are the sad realities that 19th century women had to endure throughout their lives. Therefore, Maupassant does not necessarily criticize Mathilde, but the limitations imposed upon women like her, when in reality there is very little that these women can really do to make their lives better.

If Maupassant were harshly criticizing Mathilde, he would have juxtaposed her to a husband who is highly engaged in his marriage, or crazy in love with her. He could have made her into a thief, or into a careless friend who may have done nothing to return the borrowed jewels. There the author would have had a great opportunity to show Mathilde as a very mean woman. Rather, he shows her as a clueless woman, perhaps as a silly woman, but more like a product of her time, of her society, and of her upbringing. The criticism is against those factors, rather than the woman herself.

Interestingly enough, Guy de Maupassant attempts to use a non-judgmental narrative style that bases the indirect characterization of his characters entirely on their actions. However, he cannot resist playing with words and attributing hyperbole and other allegory to specific dreams of Mathilde, her behaviors, and her thoughts.

The author also narrates and describes the actions of the characters under a light that reflects their personality flaws: they are either too simplistic or too complicated; too satisfied (the husband) or too dissatisfied (Mathilde). Since actions speak louder than words, clearly Maupassant wanted his characters to "do the talking" for him. 

In "The Necklace", however, being a Realist novel, Maupassant manages to put some of this emotions on the surface, not necessarily criticizing Mathilde herself, but women in general. Marriage is also criticized, social relations, and the hierarchies that make up the social classes. 

As far as criticizing women and marriage, notice how Maupassant already takes jabs at the two from the very start:

The girl was one of those pretty and charming young creatures who sometimes are born [...] to clerks. She had no dowry, no expectations, no way of being known, understood, loved, married by any rich and distinguished man; so she let herself be married to a little clerk of the Ministry of Public Instruction

The tone used is, therefore, is very ironic, highly sarcastic, and very indicative of several things:

1. Women have no choice in society but to marry
2. The lower classes do not often have "pretty and charming" daughters
3. Marriage is a business transaction. No money, no good prospect.
4. Clerks are "little" in value
5. Being married to a worker of the Ministry of Public Instruction (Maupassant was one) is a lowly marriage option. 

Throughout the story, we see many more examples of this tone and criticism of Maupassant. However, remember that he also juxtaposes the issues with his characters to their realities: there is very little people without resources can do when they face a situation. Money would have helped ease a lot of the situation. They did not have the money. Circumstances were less than optimal for them. Therefore, there is still a degree of compassion to be had that does not entirely put the character under a uniquely negative light.