[Butch Cassidy Slept Here]

Complaining to the Irish airline regulatory authority, as well as to the Aviation Consumer Section of the US Dept. of Transportation, is one of the few things you can do. Send "carbon copies" of your letters to Delta. Don't waste your time writing a separate complaint letter to Delta. Delta will be very quick to seize upon the point that they're not responsible for the information (about the importation of pets into Ireland) they give-out. Beyond sending you a form letter acknowledgement there is probably nothing the government agencies I've mentioned can do in the way of redress, or compensation, to you.

I don't have a very high opinion of Aer Lingus (Irish International Air.) However, in this instance, putting-up with the attitude of their flight attendants might have been a worthwhile price to pay in return for allowing your pet aboard their aircraft (for a fee, naturally!). I note Aer Lingus does operate one daily SFO - DUB non-stop. Unfortunately, your travel agent probably is compensated better by Delta than Aer Lingus.

Based on your story it sounds like Delta was, perhaps, making-up things as they went-along. Delta's story seemed to change three times during the course of your interraction with them.