We had a butterfly themed party. It was easy. I made butterfly bunting, out of cardboard, string and a hole punch. I bought paper plates, cups and serviettes with butterfly pictures. There were butterfly wings for all the guests that I bought cheaply from somewhere.. It was easy.
In the party bags a put a small butterfly toy and a chocolate.
If butterflies aren't you dd's thing, you can pick any animal you like. Try eBay if you can't find the serviettes or plates in your local stores..
I hope that helps!