Im not sure about the ranking of hornsby girls (although i know that abbotsleigh has a high ranking), but this is what minai had to say (im not saying minai's word is the be all and end all but it's interesting)
"The ranks are BS from SMH because they ranked based on number of merit list mentions, so obviously larger schools will be ranked higher
The Daily Telegraph ranks are more accurate because they take the merit list mentions, divided by the number of exams sat, which makes it fairer for smaller schools"
Also, this is what someone else said: "but i reckon the SMH rank is gay coz they don really take into consideration how many students are actually in a grade... coz a grade with 150 is totally different to what 120 can get... theres more chance coz they got more students... blah blah
either way go the Daily Telegraph..."
Now, I would take the SMH over the DT any day for news reporting but for this ranking thing...hmmm