It sounds like you're going for ease of use rather than just easy games. Is that correct? In either case, I third Animal Crossing.

Also consider WiiWare titles like Bonsai Barber,  the amazing-and-overlooked Art of Balance, the multiplayer-fun Defend Your Castle, the dancing game Helix, and the new WarioWare D.I.Y. Showcase. Oh, and of course Tetris Party. All of these have pretty basic controls, although I most strongly recommend the latter three depending on what type of game she'd be interested in. Defend Your Castle should be your top choice if you plan to play with her.

Anything with wii in front of it.

NSMB wii definitely if you're willing to play with her. The game's mechanics are simple and as long as you tag along, you can keep popping her bubble.

Also, carnival games, and party games are also a lot of fun/simple.

That sounds so icky...

You should probably check out Klonoa, an awesome 2.5D platformer, plus it's very easy to get into and it's pretty cheap nowadys.

Monster Hunter Tri... jk

Wii Sports, Wii Fit, Endless Ocean

Just Dance, its stupidly easy and great fun and also a mild workout, get it!

Nintendo have annonced wii party, can you wait for E3 ?

Kororinpa: Marble Mania is an excellent and easy to learn game.

My biggest successes with older women were with Boom Blox, Jewel Master: Cradle of Rome and Just Dance.