So don't hate on me guys for my car choice because I'm just providing my experiences for the sake of analyzing the OP's question. I am providing this not to try to convince you to buy such an expensive car but because I found the same observations when I was searching around for my subaru. My recommendation for someone like your GF, who probably doesn't care as much about her ride as I do, is a used corolla/matrix or civic around mid 2000s years 50k-100k miles. This is probably what I would have bought for myself if I wasn't a crazy person.
I drive a 2015 WRX and today, when I search for the same exact car I have with the same options, I see cars with 15k-30k miles selling for very very close to what I paid.
I'm talking about these types of numbers:
NEW: $28,500
Used: 21k miles $26,900
Used: 26k miles $27,175
Used: 25k miles $27,698
Used: 16k miles $28,500
Used: 17k miles $28,270
Used: 23k miles $28,888
This is with a nationwide search for this car used with 15-30k miles sorted for best prices.
I am NOT claiming that a WRX or even a subaru is a mustacian car, but if you are going to buy one anyway, I can totally see a justification here to buy new. The depreciation here seems to only be around 5% for the 20,000 miles driven and to me, 20,000 miles is more than 5% of the car's reliable life unless your planning on driving past 400,000 miles.
I've done this analysis multiple times and always found that cars all across the subaru lineup hold their value extremely well especially in cold climates and there can be some value attributed to having a new car, especially if you are a car enthusiast.