The easiest thing is books - does she already have recreational maths books? There are some threads around here about various ones. My DS adores all the Murderous Maths books (some parents of girls consider them too boy-humoured, but I also know girls who like them); The Number Devil and the Adventures of Penrose are also worth looking at.
Alcumus is free and fantastic, but if she's 7 and not particularly ahead that's probably a recommendation for in a little while rather than for now, though.
There are quite a few good websites, of which the most obvious for your DD right now is probably
nrich.
Any kind of logic puzzle, sudoku etc...