This sounds like the proverbial straw that broke the camel's back. You're right, it isn't really a big thing in the long run - just right now. Go fix yourself a cup of tea!
It's a disappointment, yes, but this happens a lot - perhaps especially with secret santa-type gift exchanges.
Maybe you and your daughter could sit for a while and think about what *might* have happened at her gifter's (is that a word?) house. Maybe things have been awful there, and the plate was the best she (or her mama) could do, despite the guidelines. Maybe the girl's family just isn't big on the whole secret santa thing, and this was a burden. Maybe the girl forgot to let her parents know about the gift exchange until the last minute. (I'm surely not the only person in the world who did that as a child. Even when teachers or troop leaders would hand us notes to take home to our parents, I would forget to give the notes to my mother. At the last minute I would remember and say, "Oh, I need a present today..." or "Oh, I need three dozen cupcakes today..." It's a miracle that I lived to grow up.) You'll never know for sure, of course, but sometimes it can help put mistakes like this in a better perspective.
Lessons to be learned: Things don't always happen the way they ought to. That's the kind of planet we live on. It's good not to put too much store in what you MIGHT get from somebody. And it's good to try not to keep score - "look what I did for you, so you should have done the same for me." Your daughter's recipient received something she (hopefully) liked, and that means your daughter is learning how to think about someone else. That's worthwhile.
As for the plate, just put it somewhere out of sight and forget about it for a while! In 2012, when emotions are on a more even keel, give it to charity.