There is a lot of good advice on the other website you have referred to.
I'm not sure what you lose by a review - I know that in theory, it is supposed to prevent you then from making an appeal, but there is so often a procedural mistake which will then allow you to query the review and go to appeal. I suppose the only reason that I wouldn't, would be if the school work was not of a very good standard - then it might be better to hold your nerve, carry on working and try and show a big improvement by appeal time.
Not that it will help, but the level of the mark doesn't relate to relative difficulty year to year, but is a function of how they standardise in Medway and how many took the exam - so sadly it doesn't mean your DD would have passed in the past three years.
I suppose one argument against review is that the RGS entrance mark is almost invariably higher than the pass mark, and if your DD was passed on review, she would get the pass mark, nothing higher. Two years ago they took all the girls who applied, even those who passed on review - but that was the smallest year of applicants following a run of lower birth rates. We are now on an upward curve, (and I think there are more applicants from Kent), so I would expect the entrance mark to be above the pass mark.
Presumably she also took the Kent, unless you are really OOC, so you still have another chance?
Good luck with whatever you decide.