Find the best bang for buck used that she'll enjoy driving. Something 4wheel drive and reliable that she'll feel safe and confident in. Make sure she thinks its at least "cute". Don't spend a dime more then you have to as it's a depreciating asset that will depreciate faster with a woman behind the wheel. This way, when she writes it off doing some dumb **** because she has absolutely no situational awareness when shee's driving, it will hurt a lot less than if you bought her the brand new Mercedes her ego wanted.