More thoughts about this.
If the "lady" that walked in to the "We Buy Gold And Rip You Off" place (or pawn shop) never mentioned the word "silver, silver round or silver bullion" then the buyer assumed it was silver rounds without verifying the actual metal content and made a real stupid mistake. A prosecutor is going to have a tough time proving that she defrauded the buyer. All she has to say is "they never asked me what they were and they made me an offer for my pretty junk metal and I took it."
This is similar to those guys selling iPads out of the trunks of their cars at the gas station your filling up at. They show you an iPad and have unopened boxes laying in the trunk. You give them 100$ and pick up a new, shrink wrapped box and scurry back to your car feeling real good. You watch your rear view mirror as you drive away anxious to get home and open up your new treasure. You open the box and find a piece of wood the exact size as an iPad. You now gonna pick up the phone and call the police?
Of course she is a crook but this sure looks like this one of those incidents where one crook got the best of another crook. Bye bye money.