Sweet Jesus!
That is why I do not let my children access to the net unless I am with them - PERIOD. But I am not delusional... eventually they will see these things too. Especially as my oldest gets older, so too will the youngest (get what I am saying?).
She'll be ok. Trust me, there are worse things....
ie - A child being shown an artistic nude of her mother by her father while he is pointing to the pic and saying, "See sweetheart - THAT IS WHAT A WHORE YOUR MOTHER IS." (The child was NINE.)
This too shall pass. Just take the opportunity to try and turn a negative situation into something positive. Discuss human sexuality, the difference between love and a mere sex act, birth control, premarital sex - whatever. Don't just put your head in the sand and pretend it didn't happen. Your child is looking TO YOU for guidance - now, as in the past, and certainly forever into the future!