Congratulations, either way you know your daughter is going to a good school.
In a similar situation my dd opted for Prendergast simply because "the people were nicer". I am happy with that decision though as school is slightly closer and her friends will be around the same area as opposed to Kingsdale's far flung catchment. After the "everyone's invited" unveiled the scale of sexism/abuse in schools I'm also happy that it's single sex although there are benefits to mixed and I think now that the issues are being discussed more openly that's a good thing.
It's a bulge year this year so 150 girls joining, I'm hopeful dd will find her cohort among that number.
I'm not sure how different the curriculum is, Kingsdale appear to offer Latin & Economics extra though not sure if they do Sociology. Probably worth checking that out and if the difference is meaningful to your daughter. Agree the plethora of extra curriculars offered looks great at Kingsdale, though Prendergast looks pretty solid there too (there's only so many days in the week).
I prefer the Prendergast Head. I don't like the Kingsdale Marketing/Sales pitch, selling so hard knowing that only a small fraction will get in doesn't sit well with me ( although I would still want a place at the school if I didn't have another offer.....)
I've only ever heard positive comments re Prendergast.
Sorry no solid experience to help your decision but as our situation was similar, thought I would share. Good Luck, I am sure she will be happy with either school.