Money issues bring out the worst in people sometimes. There are stories about it concerning my Dad's side of the family and we also helped my mom for a while (by taking over payments/buying the condo her parents were living in) and it was a big scene when we said we now have children to take care of, it is time for my grandparent's children (as their oldest grandchild--I had done enough), to assume this mortgage.
You have sons in or about to go to college--it is so expensive even when they have partial funding (scholarships rarely pay for room and food). So even if she was a saint she comes in third on the priority list for your funds. When I see how this thread has evolved--I really do think you may be getting to the point that you might be able to mostly stay away from her. I think what is hard for you is that family momentos/history mean a lot to you. The fact that your mom wants to sell that necklace means that her intention is to preserve nothing from your family history for you. If she was understanding of your feelings she would have considered your loan as payment in full for that necklace. Based just on that, don't count on anything, including there being any equity left at all in her place when she dies. This is just what happens to people who were, for whatever reason, are unable to robustly fund their retirements. I know you know this and it hurts but restating this might help you stay away from her.