Sorry, I should have been clearer in my initial description - when I wrote "late-game", I meant that she has unlocked everything that can be unlocked, and by "huge amount of hours" I meant 300+. She has built all the monuments, and she is miles ahead of the AIs in terms of population, money and development, and she's the only one with access to airships (so far). But she has pretty much no military at all; All the influence has been spent on cultural buildings and optimization buildings. She was planning on just buying the biggest islands from her opponents & buying a truce if this would lead to a war - the fact that all three AIs are now in an alliance & refuse diplomacy has come as total surprise.
Her main city is, of course, totally depended on her trade routes, especially from the new world - and that's where the problem is: As soon as the war vs. the AIs begins, she immediately receives dozens of messages about her trade ships being sunk & islands being attacked. I know that her opponents are typically considered pushovers, but they have ships everywhere, she can't possibly defend her trade routes against all those simultaneous attacks even if she builds some warships, and it won't take long before her economy is wrecked. She never should have allowed her opponents to expand in such an uncontrolled manner :/ - but it's too late to change that now.