Q: My daughter and I were booked on an Aer Lingus flight from Paris to San Francisco via Dublin last year. Our flight from Paris was delayed — due to fog, we were told — and even though we arrived 15 to 20 minutes before the scheduled departure of our connection, we were told that the flight had “already departed.

An Aer Lingus representative told us to go downstairs and “get sorted out.” We waited in a horrendous line for seven hours. I’m not exaggerating.

When we finally got to speak to an agent, we were told that the flight the next day was “full.” I don’t believe that this was true, because while in line I checked the flight online and there were still tickets, albeit in business class.

An agent confirmed this, but said we could not have these tickets because they “had to be kept open.” Aer Lingus ended up putting us on a flight the next day to Boston, where we had a stopover of five hours, so we did not arrive until 10 p.m. Saturday. Our scheduled arrival time was 3:30 p.m.

I also was out of my medication and told Aer Lingus that I had to get home. The gate agent snottily said, “Oh, perhaps you’d like to skip this flight too and go to the hospital?”

I personally believe Aer Lingus overbooked the flight and did not want to treat us as “bumped,” because then the airline would have had to compensate us. The agent at the gate in Boston told me to contact Aer Lingus, which I am trying to do, but I am also exploring all channels for help in this regard. I do not fault the airline for the initial delay, but I do fault it for what happened after that. Nora Rousso, Los Gatos, California

A: You’re right, Aer Lingus’ initial delay, caused by weather, was not its fault. But what happened afterward — the denied boarding, the seven-hour wait, the one-day delay — well, let’s just say the airline could have done a little better. OK, a lot better.

It looks like you fought the good fight for compensation from Aer Lingus, but you made two mistakes. First, you asked for compensation without citing any rules under which Aer Lingus would be required to compensate you; and second, you were very persistent — borderline pushy.

Next time you run into a problem like this, remember to cite any rules under which the airline is required to help you. For domestic flights, check out the airline contract of carriage — the legal agreement between you and the airline. In Europe, there’s also a regulation called EU 261, which requires airlines to compensate customers in the event of a long flight delay. When you contacted Aer Lingus, you cited its contract of carriage but not EU 261. Also, bear in mind that brief, polite emails work best, even when you’re upset — actually, especially when you’re upset. Angry, threatening missives are routinely ignored, even when they contain absolutely valid requests.

And your request, simply put, was valid. Little did you know that EU 261 applied to one of your delays, which I discovered when I contacted Aer Lingus on your behalf. I think you could have appealed to an executive at Aer Lingus (elliott.org/company-contacts/aer-lingus/) and achieved the same result, as long as you knew what to ask for and as long as you asked for it in the right way.

Aer Lingus said it was “very disappointed” to hear about your flight experience and cut you two checks for $647 under EU 261, as well as $113 for your additional expenses.

Christopher Elliott is the ombudsman for National Geographic Traveler magazine and the author of “How to Be the World’s Smartest Traveler.” You can read more travel tips on his blog, elliott.org, or email him at chris@elliott.org.