Why do you think Mme Forestier never contacted Mme Loisel after the return of her necklace in "The Necklace"?
When Madame Loisel returns the replacement necklace, Madame Forestier "said, with an irritated air:--You ought to have brought it back sooner, for I might have needed it." This irritation might explain why there was no further contact between the two women. They had nothing in common anymore anyway. Madame had probably suspected that her former friend had no intention of returning the necklace, and she might have decided she wouldn't ever lend her anything again. There is a gulf between the rich and the poor which makes it impossible for them to maintain friendly relations. Madame Loisel was terrified that her rich friend would examine the substitute necklace and discover that it was not the same one. That in itself would prevent Madame Loisel from contacting her friend again. And Madame Forestier had no special motive to condescend to contact Madame Loisel. The Bible tells us that even the poor man's relatives hate him, but the rich man has plenty of friends. The necklace was a source of misunderstanding and misfortune, like a lot of material possessions. There have been many stories about how jewels lead to crimes including murders.
It never occurred to me that Madame Forestier would ever contact Madame Loisel; she did not visit her before Mathilde borrows the necklace, and I see even less reason for her to do so after it is returned. They are long-ago acquaintances at best, and the fact that she shows no sympathy for Mathilde's needless sacrifices makes it clear she will not go visiting. Anyone who keeps the real jewels and does not offer to return them--or somehow compensate her for the difference--is not a nice person. Despite the fact that she loans a necklace (which is not worth very much, remember), she is greedy and selfish, looking down her nose at a former friend. Mathilde should be glad Madame Forestier does not come to visit.
"Oh, my poor Mathilde. But mine was only paste. Why, at most it was worth only five hundred francs!" (appr. 7 francs/a dollar)
Considering the implied tone of the words of Madame Forrestier, she has not been worried about the necklace that she has lent to her old school friend. This nonchalant attitude of Mme. Forestier points to the contrast of the two characters: Mme Loisel is indeed interested in material objects, and, therefore has put an exorbitant value upon it while Mme Forrestier never has given the necklace a second thought.
I think that it is agreed that the situation would be way to awkward for everybody involved. It is interesting, though, that we see a hint of cultural infusion in the way that these women, whom knew each other from convent-school, had a "matter of fact" attitude when it came to material things, borrowing, and returning. It may be a cultural thing, but there is little warmth between the women after the affair of the necklace. One would think that they would be supportive of each other, and that there would be a lot of sympathy in love, but no such thing.
Nevertheless, if you look at #1 you see the gist of everything: Mdme. Loisel felt despair, regret, anguish, and vexation. I think that would be my case if I had been in her shoes. Imagine the most embarrassing moment of your life, the biggest loss of money you ever had in your life, and the most foolish you ever felt in your life...and combine them all into ONE- which was supposed to be a happy moment for you. Deep stuff!
It could be a simple case of snobbery. Sometimes those who reside in a class wealthy enough to allow a woman to wear a necklace that looked as expensive as it did look down on those who don't belong to the same caste in society. We all likely know people who used to be our friends, but then got rich and forgot who we were.
I imagine that Madame Forestier felt bad for Madame Loisel. I imagine that the two of them had mutual friends and Forestier found out about Loisel's increasing poverty. I imagine that Forestier did not know why Loisel's circumstances had gotten so much worse. Forestier would probably not have wanted to visit Loisel because she would know that Loisel would feel very bad about having others see how far she had fallen.
We are not given a direct answer to your question from the text, and so it is up to us to infer what we can from the text and try and come up with a credible response. However, I think a very important clue that the text gives us can be found at the beginning of the story, when Madame Loisel's life and daydreams are presented to us and in particular the shame that she feels about the low social status that she occupies:
She had a well-to-do friend, a classmate of convent-school days whome she would no longer go to see, simply because she would feel so distressed on returning home. And she would weep for days on end from vexation, regret, despair, and anguish.
We can imagine, therefore, that Madame Forestier already felt that there was a distance growing between them even before the disaster of the loss of the necklace. How much more ashamed of her situation in life would Madame Loisel be after she has sunk even further into poverty? In addition, note the way that Madame Forestier responds when her friend returns the necklace:
When Madame Loisel took the necklace back, Madame Forestier said to her frostily, "You should have brought it back sooner; I might have needed it."
The "frosty" response she recieves is yet another further indication of the distance that is there between these two old friends. No surprise then, that Madame Forestier should not seek to contact her old friend until they have their fateful meeting at the end of the story.
Because they were distant when they gave her the necklace and keep paying it. In my opinion it was because of that.