From the operations manual,
"An Aircraft Commander may, at his discretion, in consultation with his crew, extend a FDP beyond the maximum
Gyro Nut, just to clarify, this is from the
flight deck F&D limitations. The cabin crew F&D limitations do NOT include the phrase "in consultation with his crew". Therefore, unless they had a compelling reason or special circumstance that had to be taken into account, they should not expect to dictate whether the flight goes or not.
Were I the captain I would have wondered how they could claim anticipated fatigue when they had just spent two and a half days in a most comfy hotel.