Mme. Loisel does not recognize good quality jewelry. She does not for a moment recognize or suspect that the diamond necklaces she borrows from her wealthy friend is a fake, a mere piece of glass. When her friend, Mme. Forestier, tells her to look around for a necklace to borrow:

Suddenly she discovered, in a black satin case, a superb diamond necklace; her heart began to beat covetously. Her hands trembled as she lifted it. She fastened it round her neck, upon her high dress, and remained in ecstasy at sight of herself.  

Mme. Loisel is too poor to have developed an eye for jewelry, but the point of the story is that she is too shallow, too fixated on longing for luxury, to probe beneath the appearance of things. The fake, paste necklace, which glitters but has no real value, represents the shallowness of the life Mme. Loisel covets. Mme. Loisel also never questions her friend about the value of the necklace after she loses it, which represents the unquestioning way she accepts the outward form of the wealthy life as having great value. If she had looked beneath the surface at all, she would have recognized that what she desired, the necklace and the life, were worth far less than she imagined. 

No, I don't think Mme. Loisel recognized good quality jewelry. She came from a family of modest means and was married to a man who was only a humble government clerk. When would she have had an opportunity to familiarize herself with good quality jewelry? If she had possessed that ability she might not have gotten into such serious trouble. She might have recognized the necklace as being made of fake jewels. She might have borrowed it anyway, but she wouldn't have been so devastated when she lost it. Everybody senses that there is a flaw in Maupassant's story. The Loisels should have gone to the owner of the necklace and confessed that it had been accidentally lost. One wonders whether any of the distinguished guests at the ball recognized the necklace as a fake. Naturally it would have attracted a lot of attention because it would have appeared to be extremely valuable.