Girlfriend "liked" a naked photo of her friend?

[Bob]

So my girlfriend of just under 3 years has instagram/facebook/twitter etc, and I HATE twitter and facebook, but use twitter for sports news, and facebook so i can keep in touch with a few volunteering groups etc i'm involved in. i quite like instagram because i'm into photography and i like the filters etc. anyway, i am "following" her on all these sites as you do, and she is "following me". and a certain feature on instagram comes up with the recent activity of your friends or whatever, and i've seen that she has liked this photo of one of her male friends, who is a model and in the photo he is genuinely naked and it's cut off at the worst point, but still is naked. anyway, he's pulling some stupid pose, but it made me feel pretty bad because i am self-conscious about my own image as she knows, and when i asked her about this photo, she completely deflected my questions and made it out to be nothing. but i'm not entirely sure why she wouldn't think about how i would feel about it? i understand people have little crushes or w/e on celebrities or something, and we joke together about certain celebrities and how i have "man-crushes" on male celebs etc, which is all in good taste. but the very last thing i would do to her is to publicly express a fondness of a photo of a girl i knew where she was naked.

am i reading too much into this? i hate the idea of feeling like i'm trying to restrict her doing certain things, but at the same time i feel like this is a little overboard.