Enamel jewelry is beautiful and I love it. Preferences are a personal choice type of thing and some people like enamel jewelry while others would prefer something else. Personally, my thinking is I'd make sure your girlfriend would like an enamel piece. The longevity of enamel jewelry depends on the process used and the quality of the line of jewelry. I'd suggest that for that price, the piece should have some sort of 'guarantee'. While lavenderjunkie makes a good point, it's also possible the recipient of this intended gift already has a jewelry collection that includes gold and diamonds and this piece intended to be that special something different. Good luck with your choice!
In my pantry with my cupcakes...