In the end, her travel medical insurance made the decision; it could only be extended so long. AC rebooked a week or so later, no real issues.

Just curious about one point, which perhaps matters if she wants to ask for EC261 compensation: she never did get notified of the cancellation. AC says LH should have notified her. LH says they tell the ticketing carrier who notifies the passenger. So neither did. Who is supposed to or normally does?

(I do feel slightly awkward asking about that, since she would have changed the flight if it hadn't been cancelled. So it would strictly be a bonus, not compensation for inconvenience.)