OK. So, as anyone who reads my posts knows, I'm a journalist, the lowest form of pond life according to some other contributors. But the one thing companies like BA hate, is a factually accurate story about their imcompetence and bad treatment of passengers. Why should they get away with this? They've treated your partner abominably, and the travelling public should know what happened. For heavens sake, a simple check should have shown them the original flight from GLA to LCY was cancelled. It's scandalous. Contact your regional daily, local weekly, whatever, and get a story in the paper. This isn't a complaint about bad cabin service, or a delayed flight. They've all but stolen your money, and their staff in Gibralter did not give a fiddlers about customer service or the airline's reputation.
From what you say, here's what I would have written.
"Inverness-shire passenger ............ was transferred to a Heathrow bound aircraft by British Airways, when the world's favourite airline cancelled a flight she was due to travel on between Glasgow and London City last Monday evening.
........... made the second part of her journey to Gibraltar the next morning. However, two days later, when she attempted to check-in for the first flight of her two stage trip back to Glasgow, she was informed she had "failed to show up" for the London City flight
The British Airways representatives at Gibraltar Airport also told her all monies paid to the airline were being confiscated because of her failure to travel on the cancelled service, and she would have to pay BA £.... if she wished them to transport her back to the UK.
The representatives refused to listen when ........ attempted to explain the flight had been cancelled by BA, and she was forced to travel back on an aircraft operated by another carrier at a cost of around £400."
The journalist writing the story will throw in a few quotes, and will have to contact the BA press office for a statement.
Believe me, unless things have changed drastically very recently, you will not wait four weeks to hear from the airline.
The reason why airlines and other organisations don't take this sort of thing seriously, is because it's very rarely made public. Instead, people rely on discreet letters which, as you've been told, may not be answered for some time. What contempt with which to treat their fare paying passengers.
Sorry, but even writing stories about people being treated this way makes me so angry.