Okay, I can offer a little Audi advice:
Audi A4 (This is also called the B7 ?)
Avoid getting a FronTrac CVT A4 2.0 car, since the transmissions have issues, make noises, and customers generally didn't like them. Most 2.0-liter front-wheel drive A4s were CVTs, so be on the lookout for that. There's no exterior badging to let you know the difference, but you'll feel the difference once you drive it, because you won't feel any upshifts/downshifts. Maybe she'll like the CVT, but they did have issues, and I replaced roughly one a month for Audi customers because they (the car) acted weird.
Now 2006-2008 2.0 A4s (both quattros and non-quattros) with DSG automatics are some of the best there are; quick up and down shifts, and they usually have the paddle shifters, which actually allow you to step in at any time and override the automatic settings. The DSG tranny is the best of both worlds, since your intended choice must be automatic.
The performance difference from a 2.0L I4 turbo to the 3.0-3.2 liter V6 is negligible, at best. See for yourself.
The S-line trim package have extra visible features, but no added performance benefits other than available 17"-18" tires.
1) Look out of transmission issues on CVTs, avoid CVTs altogether, in my opinion.
2) 2007-2008 2.0-liter A4s may have oil leaks and also oil pressure issues. I no longer work for Audi, but this was a big issue with their cars; low oil levels and pressures were detected. Non resulted in a dead motor, or anything catastrophic, but a few had oil leaks that were probably related to it. The funny thing was, most people who really drove their cars hard never had this issue, so said the owners. There may be a fix by now, since people were infuriated with this problem, which was also on 3.0 V6 Q7s, oddly enough.
Interior surfaces are generally good; leather seat trim holds up pretty good compared to a lot of other cars I've seen. But there's three common issues that go wrong, most well before the warranty has expired:
1) The A/C and radio buttons have a painted surface that peels within the first 3 years and 30,000 miles on every car, so if you're within the 4 years/50,000 miles of ownership, the dealer will replace the console for free.
2) The glovebox lid my not close, or not open.
3) Center armrest lid has a habit of breaking off.
If she wants the convertible, the top is always problematic in this car. They leak and tear easily, especially around the rear glass window. They are not cheap to replace, either.
Audi TT
I'm assuming you mean the 1999-2006 model years. They are fussy cars, and can be expensive to maintain. The steering is a lot heavier than you think, so it's not the "chick" car that everyone imagines it to be. The interior is a little quirky-shaped, with little room for much of anything to stash things.
They can be expensive to maintain, but I had several that were over 100,000 miles. The owners were a dedicated bunch, much like the original Lexus SC owners.
Get to know a technician at an non-Audi shop that knows German cars, if you're out of warranty.
Alternate Suggestion
I'm going to throw a late-2nd-generation or even 3rd-gen Lexus GS 300 into this mix: Not the most powerful of things, but you have a C230 and TSX on the board, so it has much power as they do. Good chassis response, they're absolutely bulletproof in terms of reliability inside and out (a few early factory campaign issues on the '06 GS 300). No really, they are fairly trouble free, and Lexus owners are a discerning bunch when it comes to the fit and finish and noises and reliability of their cars.
Sometimes a GS 400 might fall into this, it has the V8, and are comparatively rare. Car & Driver named them 10 Best from 1998-2000, as a plus. Cons are that she might be associated with an older crowd (although we had some young GS drivers), and it's looks are polarizing; some think it's weird, some think it's unique and classy. You didn't completely rule out Lexuses, so I thew that out there. It's also a little bigger (though not by much) than a C-class.
Do not bother with ES 300-330, maybe an IS 300 (old one) or IS 250-350 is more her thing, though. IS 250s are not that quick for the money, though they are feature-rich.
The Others
My brother-in-law has a G35 sedan, and 70,000 miles later, he has no issues. Nice car, better than the GS in some ways. I've nerver driven the coupe, but I tooled around in a 350Z once, on a test drive. More of an obvious sports-car flavor. Miatas are good, but an automatic just spoils that car's flavor. Sheesh, my sister even learned how to drive stick in order to enjoy one to its fullest.
The TSX is nice, ask Duke. He's the expert on that one.
Well, the Civic will save you some money compared to the rest; if she wants any performance, the 2007-Now Si is the only one that will do; two or four doors available. Maybe she'd like a VW GTI, in that case.
I drove an 2008 Jetta for a week, and it's basically a Corolla with a VW badge, save the DSG. Nothing radically special, unless you plump for the GLI model, then it becomes attractive.
I don't have any reservations on the BMW 3 series, but compared to a Lexus IS series, it's really the same car, although BMW offers more handling packages, and is a little more track-oriented. If those things do not and won't matter to her in the future, it's a push.