Here's what I'm looking for:
- the illness needs to begin before they board the flight, hopefully with symptoms that could be dismissed as a minor health issue.
- it needs to become worse over the course of the flight. The flight itself is from Canada to London, diverting in Scotland. I'll choose the departure city depending on the length of time I have for this progression from 'minor symptoms' to 'we have to land ASAP or she might die' but 6-10 hours is the current range.
- it cannot be solved with the existing medical kit on board (see here for such a kit).
- after landing, the character needs to be hospitalised for several days - she can have surgery if required - though must be able to communicate within a few days, or as long as a week. (The point is that she cannot have any serious medium-term barrier to being able to speak with her daughter about important issues, but she can't leave the hospital.)
- there will be some medical person as a passenger on board to give advice. It doesn't have to be a fully-fledged doctor, but if not, they'd contact some kind of ground service that gives medical advice.
- it cannot be anything that would cause a huge contagion scare (i.e. no ebola).
- it could be a development of a long-standing condition if necessary. The character is in her late 30s. The plot is such that, if the character were supposed to have long-term medication to keep an illness in check, it would be plausible that she'd have run out of it. The character could also think "oh, I will be safe getting on this flight and just deal with it when I arrive" and then it accelerates. (The character travels a lot, so "ignorance of the impact of air travel on this condition" would not be an excuse.)
I've checked various pages about medical emergencies on board, but while I can find some statistics (only 7% of medical emergencies needed diversions, for instance), and general discussions about emergencies/diversions, I need something pretty specific.
I was thinking appendicitis that develops complications, as it could be dismissed as a bad stomachache at first - would that work? Any other suggestions?