I'd definitely recommend you try to keep the cat in a carrier, sprayed down before your trip w/ some Feliway to keep her more relaxed. Leave the carrier out now so she can get used to it and view it in a non-threatening manner.
It's dangerous for you, the cat, and other drivers for her to be wandering around under your pedals, or up on the window obscuring your vision. If you are in an accident, her best chance of surival is to be in a carrier, strapped safely behind the seat belt. However, that being said, some cats will go wild if trapped in the carrier to the point their crying and digging to get out can be more dangerous as it's impossible to pay attention to the road! None of us like to see our cats distressed to that point. I have had a few who sit quietly in the seat beside me, crouched down up in the back of the car above the seats, or rest quietly on my shoulders behind my head (makes a great head rest). I'd suggest the carrier 1st, letting her out only as a last resort if she goes nuts. Make frequent stops and allow her to explore the car/exercise outside of her carrier. None of my cats has ever used a litter box, eaten or drank water on the road even on extremely long trips. It seems like that urge just shuts down. But other cats do so keep a fresh box and some food available for your stops.
I've traveled (and moved) a great deal w/ a great number of cats. They each respond differently. In the vast majority of cases, they prefer their carriers to be in the front seat beside me, facing me. They like me to stick my fingers in the carrier and touch their paws lightly. They like the carrier to be covered w/ a blanket to minimize the scary lights and visuals of other cars and trucks whizzing by. Make sure she doesn't get too hot w/ a blanket over the carrier, keep the lower front portion unconvered. Try singing to her or talking or whispering throughout the trip. Try to act as normal as possible even if she panics and starts YOWLING. Keep the music down or off if you can.
I tried Valium once that was prescribed by a vet. I hated seeing them drugged. The whole experience scared me and I won't do it again. However, drugs are always an option if your cat has a really hard time.
Good luck!