That's the annoying thing - her previous doctor DID prescribe it on the NHS. Apparently it comes down to the doctors opinion - no proper rules and regs around it. Her new ( soon to be old ) doctor just doesn't agree with it.
Have never used Diazeoam for flying but can see why others would. A very good relaxant once on the plane is a hefty dose of Night Nurse and two or three wines, makes long haul flights much more comfortable.