A petrol gift card, or if shes travelling on public transport some bus passes or soemthing?
I didn't even think of that! I took the train/tram into the city everyday for 3 months, it does get very costly then DH would drive in at night spend a couple of hours there then drive home so we did there and back in the car also (plus roadtolls as we are in Melb).
We had $200- worth of petrol vouchers and they didn't last long (especially since we had to travel in the peek of the petrol prices last May-Aug).