She dreamed of the finer things in life. She wasn't satisfied with what she had or what her husband had to offer. Instead of wearing natural flowers she wanted jewels. If she would have worn the natural flowers and not asked her friend to lend her jewels then she wouldn't have had such a hard life after the ball. Or if she would have just told her friend that she had lost the necklace her friend would have told her that it was just costume jewlery and she would have saved herself years of hard work and money.
Maathilde is a classic case of pride going before a fall. She 'lost' her friend's necklace then lost everything in an attempt to replace it. In the end, ironically, it wasn't a big deal and never would have been. It would have been different if Mathilde had been honest from the start.