Just went through this process with my soon to be wife. We had the same budget and were looking at the same types of things your sister seems to be wanting in a car. I would suggest going with a Hyundai Elantra. I just purchased a brand new 2013 Limited for 21k after negotiating a bit. It gets ~40 mpg hwy/30 city from my current tests and has heated front/rear seats - leather - bluetooth - sun roof - basically fully loaded for that price (besides navigation... but who needs that).
I would highly suggest it! It's a great car with a ton of space! You can easily fit a 6' adult in the back with leg room. Great bang for your buck. I would definitely go test drive one and sit in it to see for yourself. I wasn't sold till I went and saw one in person.
** Seems that I missed the SUV/Sedan part, if that is the case I would look at the Sonata if you do want the extra room. You do sacrifice some MPG though for it though and the price does jump a bit.
Last edited by Satalite; 02-17-2013 at 10:11 PM.