I still stand with the credit card not being liable. There was no fraud when she booked the cruise. But you make good points about them leaning on the merchant.
And as we read the thread replies, it worked. Or something did. Carnival did offer the dummy a refund. Replies said she declined it since it was not the full amount. You’re correct; Carnival is allowed administrative fees.
That's not the point. Both the merchant and the seller agree to terms in using the credit card to use the credit card company to arbitrate disputes, which credit card companies do do. I have been on both sides. I have disputed fraudulent charges where a service was provided in a city I never visited and the credit card company agreed. I have also had someone try to dispute a charge for a service that they received. I had full documentation of the transaction and the provision of the service and won that one too.
Credit card companies are good at it for the most part beause they see it all every day.