This is so subjective... what it really comes down to is what she wants. My comments are based on my experience of owning 2 of the cars in your lineup (A4 and 325i) as well as having driven many of them (Maxima, Passat, etc)
Does she want something that will really hold up well, is easy to drive (automatic transmission and somewhat overboosted steering), and has a nice interior? Then she is probably looking at something along the lines of a Lexus or the Acura TL.
Does she want something that is a lot more inspiring to drive (manual transmission, push the envelope a little more)? Then I would say go with the Audi A4 Quattro or the BMW 325i. They cost a little more to operate over a 5 year period of time, but they definitely drive better. I have a 2000 A4 Quattro (see sig) and bought a 325i for my (now estranged) fiancee. Both are excellent cars. The BMW has a more simplistic interior, but handles slightly better and has a better motor (the inline BMW 6 cylinder engine is to die for).. it also has a much stiffer chassis and a more sports care like ride (especially if you get the stiffer suspension setup with the sports pkg). The Audi has a really nice interior, real nice lines, and Quattro is a blast to drive even when the roads are dry. Any German sedan is going to make you wish that we had 120 mph speed limits in the US because they sure as hell love to fly down the highway!
I have a friend who owns a 2001 Maxima which I have driven on a few occassions, and it doesn't have a damn thing on either my Audi OR my BMW... the interior of the car screams "econobox" ... and the handling is crap (solid rear axle suspension). The only thing nice about the Nissan is that you can get it with a 5 spd and it has a great V6 engine.
Buy the car that is the most rewarding to drive, whether that be performance, reliability, snob appeal, whatever floats your boat... when you are spending high 20's to mid 30's you should definitely get something that appeals to you, other people's opinions be damned!