@Rheafern
Grilled my ( rather uncommunicative) son yesterday and got the following, in his own words. His subjects were Further Maths, Physics and Economics.
(1) For the maths exam, revise roots, surds, quadratic equations, trig, simultaneous equations and basic algebra. I think your daughter has already done the exam right? In the interview, they ask you to CORRECT your mistakes from the paper. So, if you miss a question from the paper, try to figure out how to do it afterwards so you can be prepared for the interview. I remember this really fazed my son, because he wasn't expecting to be pulled up for mistakes!
(2)They ask about your interests outside school, what you want to study at university, and what interests you about that field and what you have done outside of class pertaining to that subject..
(3) Why you want to join City. As I recall, my son said he wanted an academic and diverse school, and one with a strong reputation in STEM. Seems to be an acceptable ans!
Hope this helps. I am sure you did not make the wrong decision with your daughter. As parents, we tend to always second guess our decisions, and god knows the expense is definitely a factor. Good luck!