Yeah I started doing things in my local area/schools, and then more established youth boards for an exam board and then different youth events/politics events for youth, from there it's quite hard to give set advice because it's so different for many people and there's no direct paths - which I also think favours those with family connections etc. Though I think more organisations which work in education (and other fields) are realising the benefit if youth boards, and so there's more of them now, which definitely helps. I did History, Politics, Sociology and English Lit A-levels, and I'm still doing my History and Politics degree.
From my youth board, I was lucky lots of the staff who worked on the company used to work in Politics, civil service etc and still had plenty of friends who also did. That gave me connections which was nice because I didn't have them otherwise. I will say all the board etc I've gotten on were open applications - so try to be vigilant for those, LinkedIn is good for that and then the direct websites of companies as well. From there I made some connection, my advice for that is just being bold, you just have to ask people, oh I was wondering if x, do you know anybody who does y?
From there I started working with a non-profit education charity/policy board(which I directly applied to and still work with) and we do all sorts from working with lots of different trusts and schools, doing events, consulting with exam boards, DfE work, other education policy groups, also building lots of skills like reports, KPIs, reporting to trustees etc. Then I'd say go to events like parry conferences, (Labour and Conservative both have youth zones, so good for meeting people etc). So now I just get to do a mix of different things and sometimes, both from searching for opportunities myself and now knowing people who get in contact with me, it's hard to balance but I'd try and yes to as much things as you can, I'm trying to go into a different area (in the next few years, for my grad career if I get what I want), as much as I love educational policy etc it probably won't be my long-term career but I do love policy work in general and may come back to it.
The civil service fast stream has a policy stream (so there's like up to 10 I think different streams you can do), and they also do an internship during university which if you can get is really good and will fast-track you for the graduate scheme application. Also think-tanks are great for internships, work experience (so I'd try and look for any online, and ask anyone at the organisations she's at about who they know) and try and get experience that way as well.
So then, you just have to go to as many events as possible, meet people, and be slightly bold - just ask for the experience, ask for the work, the more you do, the easier it is, because 1. You'll have more experience/people will know you've done x and 2. You'll find more connections.