If you created the photo, you have a copyright automatically -- it doesn't matter whether or not you filed a copyright application. The infringer can't put the photo on her website without your permission, and the ISP should respond to your concerns.

But this might be a good time to register your photo with the U.S. Copyright Office. Registration will enhance the value of your copyright and will be required if you decide to file a lawsuit. For registration forms and instructions, go to the Copyright Office website (www.copyright.gov). The fee is currently $45. Unfortunately, it may take nine months or more for the registration to go through (unless you want to pay several hundred dollars more for an expedited registration).

As to your legal recourse: You could sue the infringer, the uncooperative ISP, or both. The basis of either suit would be copyright infringement. Although the ISP wasn't the one who first stole your work, a law known as the Digital Millennium Copyright Act (DMCA) makes them similarly responsible -- particularly if they knew about the infringement and didn't do anything about it. No matter who (if anyone) you decide to sue, you will probably want the help of a lawyer who's an expert on copyright law.