Buy her a truck.
My first vehicle was a full sized GMC Sierra. My dad customized it for it. Everyone at my school my jealous, included the guys. Here I was, 5'2" and 105 pounds in a pick-up. I got out of class once and there was a stack of phonebooks on my seat because people picked on me cause I "couldn't see over the steering wheel" LoL. Funny...
In all seriousness though. What an amazing brother you are! To shoulder that type of responsibility at such a young age is very difficult for anyone to do.
It sounds like you know a lot about cars/trucks, so go with what your gut is telling you. It's better to have piece of mind, rather then a cheap car.
And no, you aren't crazy for wanting her to have a reliable vehicle.