Ds is at Warwick studying Economics which was his top choice. You need an A star in maths and entry is A star A star A for Warwick. He took maths, further maths, economics and computer science. Economics is an incredibly popular course and massively oversubscribed.
He read Freakonomics, Undercover Economist, Misbehaving and a few other books. He watched guest lectures on youtube at top unis including LSE. He did a couple of summer school econ courses, google for year 12 and see what takes her fancy. No essay competitions or anything like that. He got 4 uni offers.
It isn't necessarily about what you read/listen to/watch it is about where that led you, so for Ds he read something interesting in a book and then this led onto finding out more about this side of economics. That could be anything for your DD, so behavioural, Bank of England and the economy, wealth distribution, anything. I would advise she basically makes notes of what she discovered and where that led her. There are Econ students on youtube who share their personal statements so you can see how they did it like Sam Hillman who is at Cambridge. It is best to have lots and be able to cull down a PS than not have enough to write about. Lots of PS examples are online.
The bit I will share is that Cambridge said the PS should have wider reading and engagement with the subject, critical reflection and independence of thought. Ds's PS had I discovered, I explored, through this I found, this led me to etc while he weighed up what he found interesting. He absolutely loves Economics.