Having had two daughters pass through their teenage years unharmed (relatively), were I you, I would have sent her a nice formal letter advising her that her inheritance would be reduced by the fare differential. Obviously, "Tough Love" is easier in retrospect, but I suspect that for me (and most other parents), we miss any number of opportunities to demonstrate the actual and real value of "money".

I have a lovely niece, now married, a mother, and living on "short rations" in the UK (while her husband, his profession in reduced demand, works contracts in ghastly places like the oil fields of Libya). Back when she was a teenager, she was notorious among the family for her refusal to enter, much less shop at Kmart or WalMart. Apparently, her confrontation with reality was not only delayed, but made even more unpalatable than it might have been.

Fortunately, my dear bride, incumbent now for 47 years, was tight-fisted of necessity when I found her, did wonders in convincing our two of the perils of profligacy, and continues to shop carefully and extensively, when it comes to the timing and intricacies of our annual trips to Europe.