If it were me, I'd show her, then I'd masterbate on the picture in front of her while she stands there stunned on so many levels.
Yup, I'd walk into her office/cubicle and say, "hey, I found your naked pic on the web!" Then I'd shake hands with my man right there in front of her. I think I'd get a friend to take a picture of that (the whole scene) and then I'd post that up on the web. I'd have a nice laugh from that one I think.
/sarcasm
Seriously: I think it would be best to keep your mouth shut ... unless... unless she's getting a promotion over you, then blackmail is a bitch
No seriously though, if you're concerned for the hot biatch, she'd be better off if you didn't tell anyone.