It really depends on what kind of gamer she is. For example, if she likes watching those things to begin with then the games may be fun for her.
However, you don't say what system
for Nintendo. The WII? The DS? Are we talking old school N64?
If you're talking Wii - I always suggest Warioware Smooth Moves. (I can't get enough of that game!) I hear Super Mario Galaxy is also fun.
If you're talking DS - you may want to check out the Super Princess Peach game. Does she like Zelda? There's a pretty fun Legend of Zelda: Phantom Hourglass game out.
If you find out what system it is, and what type of games she already plays (if you know) feel free to PM me and I could get back to you asap with a small list of games she might like as well. However, you know your niece best