I've calmed down a bit now - I called AA back and while they couldn't offer a compassion fare, they did suggest that my partner's mother get to MAN or LHR to save on the codeshare fare portion from GLA. Because she is elderly and frail, I decided that it would be better for her to have the best flight for the cheapest price so I have defected her to CO because they fly to the States direct from GLA, minimum waiting time at EWR and a decent price.

I've changed my existing reservation for a future date and have been told that I can claim the change fees (total $252.60) back on presentation of a doctor's letter.

Thank you all for your kind words and helpful comments.

Aleks