I have had similar experiences with a friend. Instead of purchasing handbags that I wanted, it was clothing. She would buy identical clothes that I just purchased (even to the lengths of just a description of it on the phone) or purchasing something that I mentioned liking. We are still friends, but the competitive edge gets to me!!
I say absolutely purchase the Galliera and DON'T hesitate to wear it around her! Just remind her that you told her six months earlier you had wanted that particular bag. In the future if she makes comments like she did about you better not purchase the bag, remind her that you had already told her you wanted the bag!!