Look for a steering wheel tray table online. They’re simple but very handy.
A photo of you both for her car could be a nice touch. You could also add some hidden notes for her to find. A set of disposable wipes or small weights for a quick walk during breaks might be appreciated too.
Good cushions for her seat would be great if she’s driving that much. Back pain can be a real problem.
Fitted rubber car mats are amazing for anyone who drives a lot. They’re super easy to clean.
A portable espresso maker could make mornings on the go much easier.
You can get a small electric cooler that keeps drinks and snacks cold without needing ice. It’s super convenient for long drives.
A heated back massager could be a nice addition for long hours on the road.