What can I legally do if an item purchased at a thrift shop was taken by an employee?

I was shopping in a non-profit thrift store and there was a basket of items on the floor. I picked an item up and the person who was there offered to sell it to me for $2.00. It was a sterling silver dish. I accepted the price offering and I purchased the item. I was checked out and paid for the item 100%. Then a woman came in and took the item out of my hand. She said that they cannot sell that to me. I told her I had already paid for it. She told the woman to give me my money back and then took the item. Was she legally allowed to do that? I realized that the item was valuable and was offered an extremely low price and I appeared the offer and paid. I feel that since I paid for the item, that item was legally mine and she had no right to take it back from me.