Who is the owner of the necklace in the necklace?

MMe Forestier. It is a counterfeit wearing copy. She smugly does not inform social-climbing Mme Loisel ( la-zell it was pronounced when I had this in English) that it is a wearing copy. she loses it at the ball- exactly how is not stated- a phone call could have saved about sixty grand and a nose-dive into debt slavery and relative poverty.