There are a lot of really good vinyards in NorCal. You don't really need to spend $40 to get a good bottle. You may find that she likes Merlot, particularly if you are going to buy it and drink it, rather than buy it and hold onto it a few years before drinking.

Jordan, Silver Oak, Stags Leap and Kenwood make some pretty darn good cabs. There are so many places putting out really top shelf wine. If she is really into it, maybe get her one of those wine of the month things. They send a bottle or two every month, gives you a chance to try out a variety.