There are some meds they sometimes use to reduce strain on the heart when there are leaks. Sometimes folks with multiple heart issues can have problems with the heart tissue itself, where the valves are mounted (sewn to). While tissue valves tend to be more gentle on their mountings (at least more so than the early mechanicals), nothing is really guaranteed for anyone. Of course, it could be something with the valve itself.
She's 83. She's probably not highly active. If so, that will probably increase her ability to cope with the leak. I suspect they're going to want to try to medicate, and to avoid any surgery for her. Please let us know what they determine to do.
May it never catch up to her,