EXACTLY WHY I don't do weddings.
Perhaps a "No Zillas" sign in your establishment might be in order.
I know a photographer who has a clause in her contract that forbids brides from being bridezillas. I don't know how she enforces it, but I guess it makes a point when the clients read it!
"We contacted all of my other brides for that particular weekend and none of them ended up with the Heath Bar mousse in their cakes. I guess it disappeared into a black hole. "
Yeah, and that black hole was the mouth of all the guests...there wasn't anything wrong with that cake.
I would love to see the Brides face if you get a picture of the cake cutting... Hmmm, I wonder what she would say then. 
Jodi 
Didnt read through all the pages but in my opinion its up to her to provide proof that you did anything wrong. No proof-no refund.
I agree, no proof - no refund! Do you know what bakery she got the cupcakes from? Could you call and ask them about their order.
I think it's another case of wedding bill remorse and they want to get something back. If she calls again I would state that you will need a piece of the cake, a photograph of the cake cut to provide any sort of refund.
When I have my contracts finished one stipulation will definitely be "We do not provide refunds for consumed products." If he has an allergy that severe as a bride I would ask someone to call the cake place the day of or the day after and provide photos and proof the filling was wrong.
If it was eaten and no proof it was the wrong filling, no refund at all.
I was reading along and just had to ask how this was resolved!
Darn, I Read to the end, but there was no end! What happened?
Don't call the cupcake bakery. Don't try to find another guest who attended the wedding. Don't call the venue again. This is taking too much time and causing too much angst for you.
If she calls again (and I agree with the other posts about not accepting abusive language from her), calmly tell her that according to your records and the research you have done, it is not even possible for her to have had raspberry filling in her wedding cake. Tell her if she has proof in the form of leftover cake or a photo that clearly proves the wrong type of filling, then you will consider talking about the possibility of a discount on her cake (NOT a refund). The burden of proof is on her.
By the way, beware of how people can alter photos in Photoshop!
You should send the bride an invoice:
Charge: Cake $120 (paid on 10/22/10)
Credit: Refund for alleged mistake $120
Charge: 10 hours of labor to determine course of action regarding cake $20/hour = $200
Total Due: $200
Please remit full amount to our bakery within 14 days.
In all seriousness, she's already won. You've spent way too much time on this. In court, the complainant (plaintiff) has the burden of proof. The bride has the burden of proof. Tell her that and be done with it.
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