IMHO, the answer will depend on what she expects from the car. The E60 530i is about as good as family/managerial saloons get, and she will be hard pressed to find anything better except for the new 5 series.
The 159 can, with the 1750 or JTD, in a rational comparison, stand against the 3series or the previous A4 - but not agaisnt the 5er. It is significantly bigger both inside and out, RWD, wider track, almost 50:50 weight distribution and even the 530xi, although short of perfection as far as BMWs go, is powerful enough and sounds good enough to compete with the 3.2 Q4, while returning better mpg.
As a previous post mentioned, honestly, if she does not want the 159 because of the goergous looks, the beautiful leather seats, the originality of the design and is not an Alfa fan, there is no reason to buy it. She will be much more satisfied with the new 5 series, E serious coupe, A5/A5 sportback... Although I still don't get why she would replace the 530i.