Can you use GameShark on DS?

well, first off, a DS gameshark will not work for a GBA game . But, as long as the DS your niece owns is the old "fat" model, then she can use the GBA gameshark (meaning it will fit in the gba slot) for a GBA game in her DS. … Get an Action Replay instead if you insist, but do not buy a Gameshark.