OP here....thank you for all of the replies. I can't believe the discussion this has generated! I don't have a resolution yet, but I do have a bit more information. I misinterpreted some of the facts slightly; this was originally told to me quickly, over lunch, so we didn't spend a lot of time on it and I just got a quick rundown of the facts.
First, this WAS for my sister's church. I didn't realize that when I spoke with her on Saturday. My bad.
Second, what she received after the auction was a duplicate receipt and a handwritten note telling her to reference the church name. It also contained the donor's last name. This is what she faxed to the deli manager, and seeing the donor's name is probably what jogged his memory that the woman had been calling all week and then eventually picked up the dinner.
Third, the deli manager was quite adamant that charity donations like this are NEVER done this way. Gift cards are used. Period. He was really puzzled as to why my sister had a duplicate receipt and a handwritten note for this.
Fourth, and I will fully admit this was sister's own fault, she didn't try to claim this until Friday. It was then that they found the receipt with the so-called expiration date (which was, I believe, handwritten so was probably more of a product of the donor's doing rather than the deli's doing). Their delay was probably just an oversight since things like this (auction items) didn't generally have such small windows for redemption and through their business, they're involved in a LOT of charity auctions. So my sister called the deli and said that she didn't expect them to have turkey dinners anymore, but she had this receipt for a dinner, had bought it at a church auction, and asked if she could get some chicken or something else instead. It was then that the deli manager expressed his confusion.
Fifth, the deli manager said that the lady had been calling all during that week, not just on Thursday as I thought, inquiring as to whether or not the dinner had been redeemed. So that kind of says to me (and my sister) that she was really looking for the dinner to not be claimed. When Thursday rolled around, she used her original receipt and went and claimed it. Deli manager mentioned the last name of the person who claimed it and it was the same last name that was listed as the donor on the info that my sister got.
So, this proves that there's more to the story. My sister is not totally innocent with this in not looking at the dates better initially. I admit that, but I believe it was an honest oversight around a busy holiday, coupled with the fact that normally, auctions didn't have such short redemption periods. Alternately, it would indeed seem that the donor lady did try to hedge her bets about getting back the dinner that she had donated. I didn't want to give my sister the third degree (she doesn't know that her situation is in an online forum...LOL), but it seems as though at this point, she wants to let the donor lady know that she tried to claim her dinner and realized what had transpired with the purpose of the duplicate receipt and the donor lady claiming it for herself. She also said that she doesn't want the donor lady to get the tax credit for a donation when she really didn't 'donate' it b/c she claimed it herself. They know the person who was in charge of the auction so they're going to talk to her to see what she says about the situation.
When it comes right down to it, though, I think it still was kind of shady of the donor lady (or maybe I like the term 'Turkey Lady' better...) to 'donate' it, but then do what she did and redeem it for herself. Just the aspect of using the duplicate receipts instead of a straight gift card (as is usually done) and having a small redemption window suggests some forethought that she wanted to try to redeem it for herself if it wasn't used by a certain day.
Also, by referencing 'public shaming' in my OP, I basically meant that someone from the church should call her and say, 'hey, this is what happened. Why did you do this? Now we have someone who bought this in good faith and is out $50 b/c you ate her dinner. This is not a very Christian way to handle a donation to the church. How are you going to make this right?'