Photographer Rights

I`m a semi-professional photographer, I took photos of a female nearly 20yrs ago, she was a friend and did the modeling willingly and with her consent. I have used her photos to post on a few Model/Photography sites to showcase them in my Portfolio. There was never a model release signed by the model, and I have never sold her photos or used them in any other form than on my photographer portfolio.
She has now contacted me and has discovered the photos on a modeling/photographer site, and is demanding that I remove them and send her ALL photos and or CD disks of her photos to her immediately. She has told me that she now has obtained legal counsel, and I am wondering just what my rights are as a photographer.. Am I obligated to return her photos? and if I have never used her photos to make money directly, other than to show my work, can any legal action be taken against me on her part? Any help/advice you can give me on this would be greatly appreciated..