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Whilst I've traveled alone spending almost nothing it's not realistic to impose the same on a companion. I think the OP did the right thing getting the lady home and bailing her out financially. I accompanied a lady back to France after we'd fallen out in Spain (and I've never heard from her since).
As to what to do now, she perhaps doesn't feel like paying more than she'd expected for a romantic break that resulted in her being dumped, and the OP would like to to recover some of his cash. I wasn't there so I'm not going to say whose side I'm on, I can only say what I'd do. Which would probably be a polite letter to apologise for the disastrous holiday with a polite request to send a cheque if ever she gets an insurance pay out on the extra costs. And then let it drop.
I don't know what the relative incomes are. I more than paid my share when employed and going out with a student and I've been living on my wife's income for some years now.
Maybe my posts read abit cockish. My ultimate point is I don't think the OP is generous more careless and marks pennies owed rather than be a romantic bloke. Then dumping her.
Maybe?
I think you should shag her one last time and slip the court summons in her bag on the way out.
At the and of the day, regardless of whos right or wrong, if you took it to court it would get thrown out, you say she owes you, she said her boyfriend gifted the cash to help out, hardly an unbelievable event. with nothing in writing there's no case to answer.
A polite request for the money back is probably the best bet, but if you dumped her... I don't fancy your chances, lol.