If she loves math you should let her watch all movies made by Vi Hart. She does wonders explaning complex math. Her Wind and Mr. Ug story is very impressive.
As for games, there are several commercially available, but they are usually sectored in ages, not in skills. I would advise you to come up with a physical game, rather than a computer game as there are already tons of that. Perhaps some memory-algebra where you have 1 card with a solution and another with a complex formula.