Posting for a friend:

Her daughter spent a semester abroad returning thru JFK prior to Xmas (post the snowstorm). She had a JFK-xxx-JFK roundtrip booked on BA, then a one way from JFK-home booked separately on Delta.

Due to weather in Europe her BA flight was delayed, and she missed her Delta flight home. Delta told her that couldn't get her home for 4 days; told her to "find another airline". Her father called his amex agent who was able to book a oneway on NW for the next morning ($700) and a hotel for her to overnight as they wanted to get her home for Xmas (not sure why the DL agent couldn't see this flight, but AMEX could).

Are they only owed a credit for the "unflown" portion, or should there be someway for them to recoup the $700? How should I advise them - is calling best, or is it better for a written letter?