Sometimes in life, you have to choose between two things that aren't really good choices. You do the best you can.
For the few days of travel, feed her once you stop for the night. Don't feed her in the morning, but offer a couple of pieces of dry food every hour while traveling. It shouldn't be enough to upset her stomach, but should help prevent HL.
You might actually find that she adjusts to the car travel routine and becomes a better traveler. My daughter's cat would throw up 30 minutes into the car ride, then settle down. This time, when my daughter told her it was time to go see Talley, Harper walked right into the crate and laid down. No vomiting.
Skin kids - Jason, Kevin, Allison
Canine kids - Bennett & Bailey (always in our hearts), Riley, Banker, Rogue and Boz
Feline kids - Zoey, Talley and Abra