Hope this was obtained legally otherwise they may request its return. Usually, as previously mentioned, dies are defaced ("cancelled") by an x or something similar. However if this was just removed from the minting facilities (and sold or traded to your aunt) I understand that it would still technically remain their property and must be returned. Sell at auction? well title must be clear to do that or it can be confiscated and returned to the true owner. Lots of instances like this in numismatic items.