My ds(7) has suffered badly since he was 1. He can be sick on a 10 min journey ( and is sick on planes and boats). I know a lot of things which help but nothing than can stop it sadly.
How old is your dd? - can you distract her with games yet (eg I-spy, car counting etc) Anything to keep her looking out the window. Avoid toys books etc for the same reason. What about a personal stereo with songs or stories? Try and sit at the front if its a coach. Have a container handy (just in case) - we use a tupperware container.
Another tip is to try and put bags under her feet so that she can rest her legs on them rather than letting them dangle in mid air as this adds to the feeling of being on a fun fair ride IYKWIM. I'll let you know if I think of any thing else. You have my complete sympathy!