The fact that the Turkey Dinner was to be redeemed by mentioning TL's name, as well as TL still retaining the original receipt, TL owned the Turkey Dinner. The deli was in no way at fault, as the origin" receipt and TL's name was used to get the Turkey Dinner.
However, since the intent of the Turkey Dinner was to sell it by auction, and Sister did in fact pay, TL should have given the original receipt. TL did this on purpose. If TL wanted to keep a record of the transaction, TL could have kept the copy but give the original receipt.
It is clearly an act of fraud of TL.
If the prize was something else, such as a weekend at a bed-and-breakfast, and donor had no right to give that prize (for whatever reason), or had redeemed that prize instead of auction winner, that is a fraud.
I say tell the auction committee what happened. If they cannot force TL to pay Sister, then Sister should consider going public and/or making a police report. And then suing TL. Sister should tell the TL and auction committee this.
Afterwards, the auction committee may consider to ban such future scams, and insist GC with no strings attached in their future auctions.