Get her a bike that fits. Period. Not all women are best-served by women's bikes.

Also, with regard to the quality level--don't go totally entry-level if you want to get her into riding with you. I knew a couple with a similar story to yours, and the guy rode a Madone. What does he buy the GF so they can ride together? A friggin' hybrid. How much fun to you think she had getting dropped all the time, or getting smoked trying to keep up with the BF who's barely breaking a sweat?

I don't agree 100% with R-Wells--it doesn't need to be nicer than yours per se, but it needs to be something that you would ride too. If it's not, you've probably bought the wrong bike to share a certain type of riding.