I'm also in the camp that thinks that she probably misread or misunderstood what the boards said.

Even if the boards did say that, I'd be surprised if that had ever been the plan, and the information on the boards might have been erroneous. IANAE, but my gut instinct is that there could be a number of regulatory issues surrounding the sudden substitution on a non-EU international route of a Spanish-registered aircraft operated by an airline other than BA for a British-registered aircraft operated by BA.