PHXFlyer wrote...
if I knew that any airline had put a slag paying a cheap economy fare in a premium cabin for such nonsense I'd raise bloody hell
Delta provided the OP's girl friend with information (about entry/transit documents) they were NOT obligated to provide. The gf relied on this information, which turned-out to be wrong. As a result the gf has suffered/may suffer some damage (severe inconvenience, etc.) Buying an airline ticket should not be a game of chess. The customer, to receive the product he is seeking, should NOT have to outwit the airline. Unlike Walmart, a (US-based) airline is a public trust by virture of its certificate of operation and its right to use the public airways. Accordingly, given all the circumstances of this case, an upgrade, on a "space available" basis, does not seem unreasonable.
As to raising "bloody hell," you might want to stick to my strategy--a John Gotti impersation--wherein you cite your right to remain silent (depending on the question/comment from the flight attendant.) Picking-up on a post from Jim, the link below shows a tv interview with an American Air first class customer who dared to ask for orange juice with his breakfast.
http://cbs13.com/local/orange.juice....2.1369891.html