I moved up to set 2 from set 3 at the beginning of Year 10. I really struggled to be completely honest, as I hadn't been taught any of this stuff before. However, I think if the set I got moved to had a better teacher, I would've been able to cope but I ended up doing foundation tier for my actual GCSE because I struggled so much with all of the higher stuff. I think that it's definitely possible for her to catch up if she's bright and be able to do higher tier, but in my personal experience it wasn't possible for me at all. I ended up getting a 3 (which is the equivalent of a D I believe) on my year 10 mock for higher tier, and due to being messed around with the change of sets I had to devote most of my GCSE revision to foundation maths.
Best of luck for your daughter, I'm sure she'll be fine. It sounds a bit boring but I think it would be very useful for her to begin revising some of the higher tier stuff over her Summer holiday so that she already has a basic idea of the things that the other students in that set will already know, that way she wouldn't be at too much of a disadvantage. I'd recommend Simon Deacon on YouTube - his videos are very helpful for maths revision.