Today my sister's DD was christened along with 2 of her cousins from her dad's side of the family. At the church an aunt handed my sister a present saying it was from another aunt who hadn't come. Then she gave me one for my DD with a present wrapped in christening wrapping paper and a card that said congratulations on your daughter's christening. DD wasn't christened today and might not ever be if DH gets his way. What do I do about the gift? Should I return it with an explanation (though I have opened the wrapping paper)? Should I write and thank her and should I mention that actually DD wasn't christened and may or may not be in the future.
Is there someone else from that generation you could talk to in order to gauge how this Aunt would respond to realising/being told her mistake?
Personally, if this isn't someone you're going to be seeing regularly, (and assuming this isn't an obviously expensive gift) I'd just send a nice thank you card for the gift, not mentioned anything about a christening.
What Lynette said. Your aunt probably suddenly realised that she had never done a present for your dd, and was either worried she'd missed the chiristening, or felt that she was due her a "christening" present whether or not she was christened, out of fairness. I don't think you should return it, but a quick explanation on your thank-you note would make it clear.