With that small of a commute the TDI might not make sense for the mileage, though it does have better power than the base engine. Even with your higher gas prices unless you want to go on some huge road trips I'd say GTI. She just wont drive enough to make up the difference. Now if you're viewing the TDI as a performance increase over the base model due to its torque that works.
To help with US posters I did a quick search and it looks to be ~50 cents more per gallon for diesel over regular where the OP is.
I can't give you an exact apples to apples comparison but I'm visiting my father right now who has a 2011 Element and he tried out my 2013 Passat (5 cyl 5 speed) and he loved the ride, handling, and low down power over his car, which isn't much of a shock considering what the Element is but if she likes to drive the cars you're looking at should be even better than mine so she'll be very happy with em.
As for the Soul it's basic transportation, I test drove one just about 2 weeks back and what I can tell you is it fit most of my basic requirements but it didn't feel fun to drive at all.
I haven't driven the C30 but it seems like a great car so try it out and let us know how they compare.
Motorcycles save lives
"It's the game of life. Do I win or do I lose? One day they're gonna shut the game down. I gotta have as much fun and go around the board as many times as I can before it's my turn to leave."