Gravol CAN work with some cats but maybe divide in two (vets for some reason do not think of the dosage). I guess I do because I am used to prescribing it for young children.
The prob with cats is that as with humans, gravol (and valarian) can have the exact opposite effects if what was intended. So maybe you could try her on a small amt of gravol - if you have time to monitor her for the duration. The 25 and 50 mg tabs can be broken up into 4 sections or you can buy children's gravol since the recommended dosage for cats is 10 mg.
But there are so many other excellent alternatives out there that you really do not need gravol.
I have treated the humans in the ER whio HAVE given cats gravol or valarian and came in with the blood and the scratches to show for it. Their cat went from a sweetheart to a raving maniac in a few seconds and they were in shock and so often they would say, "But my vet suggested...". So, based on that and just what I know about my own areas of research - one of which is medications - esp for antiemetic meds for children with cancer who are nauseated. - I would never in a million yrs give my cats gravol or valarian. Any sedative really except for Cocculine - which has been studied by reputable European agencies and Rescue remedy. Maybe if they were very ill and had OCD or some identifiable psychiatric illness that required it but not for travel or something like that.
"There are two means of refuge from the miseries of life: music and cats" Albert Schweitzer