That's pretty much what I was told a few years ago. At the time, they said that they got roughly 500 or so applications, took 400 or so through to exam and around 200 through to interview, of which around 115 or so places are offered. They then have a relatively short wait list and there will usually be a few girls who are offered from the wait list.
I think application numbers have gone up a bit since then but the number of places remains the same (and applications tend to be lower than for other schools as either prep schools or parents sometimes self-select out of the process).