I don't think she can go wrong with either car. I personally love both the new A4 and C-Class. I'd want both of them in my garage.

Regarding the diesel situation, don't you guys have a diesel tax in Singapore? It might actually not be so bad to go for a petrol version then like an A4 1.8 TFSI or a C180/200 Kompressor although here the Audi will have the fuel economy advantages since its engine is much newer and has direct-injection I believe. The C180 and C200 Kompressor are perhaps a little more agile thanks to the Kompressor in my [driving] experience.