Well I think you could write to Marcopolo, because its important that they are aware of this issue, to ensure it doesn't happen again. I don't think there is any excuse for not returning to you with your meal. Sure they were busy, but they should remember, or get it straight away. She could easily have pressed the call button for another FA to come to the cart and then go get the meal. but if the FA and crew were really sorry, perhaps no need to. They realised their mistake and were very sorry.
One thing I must say, however, is that you should have been more proactive in chasing your meal. e.g if it didnt come in 5mins, ask again. Or when you saw the other FA come with the fish, you should have called out to her, saying you wanted one. I appreciate that you may have been pre-occupied though.