She should simply publish it somewhere else, such as her own blog or some other website. When she signed up to Facebook.com she ticked a box agreeing to their terms.
I never signed up so couldn't care less, but aren't most people on Facebook talking about what they had for breakfast and how awesome stuff is? I'm not sure where Napalm girl fits in with that culture except maybe "awesome war photography - thumbs up!!".
Facebook wants to be a place for news as well, with things like their "Instant Articles". It's a historically significant photo and was actually on the front page of the NY Times when it came out. So, would they censor a post from the NY Times if it had the same photo?
I never signed up so couldn't care less, but aren't most people on Facebook talking about what they had for breakfast and how awesome stuff is? I'm not sure where Napalm girl fits in with that culture except maybe "awesome war photography - thumbs up!!".