Hi all, OP here with a sort-of update.
Well, after a near-unanimous verdict here not to say anything I listened to you guys and left it alone and defriended InjuredColleague (IC).
However, when I initially saw her post I mentioned it to a friend who still works in that dept as I thought she would have seen it too and she was just as outraged by the content as I was and so she
told the manager.
So it's out there now. I've not been contacted by work about any of this so I think I'm in the clear
It seems as though InjuredColleague has deleted her FB profile, so at least she won't be causing other people problems by plastering work stuff all over the internet. However, she does appear to have a second profile - I think it's old and not used any more as it is very bare - which is easily identifiable as hers and actually lists her place of employment as OurOrganisation, which is a Very Bad Thing in our world! Silly girl.
Thanks again for all your advice.