Perhaps it does not embarrass her to have nude photos online?  Or perhaps she does not know they are online?  At any rate, I would think you should tell her what you discovered and send her the link, and then discuss your feelings with her.

The nude body is often used in art and in photography, you did not mention that this was porn, yes?  Is this more artistic than pornographic? 

At any rate, you have to decide if this fits your own moral code for you.  But as for her, she has the right to feel about it however she feels about it.  It would be good though, if you are friends, to talk it over. 

Remember the saying "a friend is someone with whom you can be sincere."