An old wives tale I have heard, is sit them on brown paper, dOg!! knows how it works, but it is cheap to try

Ginger might help, also valerian if you think stress is causing the sickness. If you do think stress is the cause, you could try introducing her to the car in bite sized sessions. 1. in the car for a few mins without driving and build the time up to 10mins day by day. 2. a few short 5/10mins journeys and build that up.
Our Charlie doesnt travel well in the very back of the car, but he is very happy to travel in a safety harness on the back seat, 6 hr journey, with a short break no problem. Perhaps try moving him.
Also he travels better in OH's car than mine, not that I am suggesting you by a new car

Hope your travels with Lily improve soon. It is so much fun to explore further afield with our cockers.