I've just read a wonderful book called 'The Secret Hen House Theatre.' Pretty new, so unlikely that she's read it, with some 'school life' to make it relevant to a ten year old. It's a modern day Noel Streatfeild!
I was thinking Moshi Monsters annual, too, not just highbrow stuff. It really depends on the child and the buyer! DD loves Jiggy McCue books. And the Donut Diaries, which are hilarious as long as you're not too squeamish about poo.
A lot of British children haven't read Calvin & Hobbes anthologies, which mine read & reread obsessively. If OP doesn't want to get a gift voucher, can't go wrong with C+H anthology.
My first thought was The Secret Garden. Or the sequel to The Railway Children. What's she like otherwise? If she's bookish, I think a book voucher would be better than any book, the odds are so high that she's already read something you choose. Saphire Battersea, the sequel to Hetty Feather, is very trendy. But then some bookish kids hate Jacqueline Wilson. Voucher for sure.