I remember these as one of favourite books as a child, but I can't remember what age I read it at.
The youngest I nanny for is 6, with a reading age of 7.9.
Is this too young? She hasn't seen the film of little princess, although I have it. Rather she read the book first.
Current favourites are
The Worst Witch
Midnight Library series
My naughty little sister
Its not fair (etc)series
Famous Five