I think some PP are being a bit harsh on OP.
Yes, technically she is not "entitled" to any of her MIL's things. Technically, the settling of the estate/who gets what/what gets sold is not really anything to do with her and she has no right to be upset by what happens.
However, I don't think OP is being entirely unreasonable here- I don't think her main point is that she feels that she should have been given a valuable piece of her MIL's jewellery and is really miffed that she wasn't.
My reading of the OP's post (and clarified by her subsequent posts) was that the value of the item is actually not that important to her. What she was hurt by was the implied lack of value placed on her, given the poor state the necklace was in and then being told that there was another necklace of greater value which she could have been gifted but that she was not to be given that because "it was worth too much to give to you" that is causing hurt.
IMHO giving your wife/SIL a tangled, broken and dirty piece of jewellery whilst saying "there was a nicer one, but it was worth too much to give to you" is, IMHO, pretty thoughtless at best. At worst it is downright mean.
I don't understand why they even mentioned the "better" necklace TBH. Given the other background OP has given, it does suggest a chronic lack of thought on her DH's part. I can understand why she feels that he doesn't value her- not even bothering to repair the necklace AND then implying that the other one was far too valuable to be given to her could be taken to imply that he doesn't really respect or value her much.