I'm not sure this is the best game for a 7 year old... Some of the puzzles can be rather abstract and require you to read somewhat cryptic clues.

All of this.

Check out What They Play.

If you're looking to avoid large quantities of text and long-winded plot development then I'd avoid Starfy.

Go with Kirby or Super Princess Peach instead. Super Princess Peach is great fun.

Final Fantasy. That's for 7 year olds right?
But in all seriousness I would recommend Sonic Rush or New Super Mario Brothers. Both very simple platformers with next to no reading. Or if you want to kick-start the gaming bug Tetris DS. No game is more accessible or more fun than Tetris.

Facepalm
You can't be serious...

(Back on topic)
If she likes Diego, there is a game that my little bro had once called Diego's Dinosaur Adventure (Or somethin' like that) it was pretty good for him because Diego actually talks to the player instead of them having to read text. If you can come across a copy of Super Princess Peach, I hear that's a pretty good game for younger girls.
New Super Mario Bros. or Kirby would be good too. And like theblackdragon said, if she likes Mario Kart Wii, she would probably like Mario Kart DS, it's actually alot easier than MK Wii.

(Back off topic)
@chadthegamer
I'm pretty sure that you have to be able to read pretty well to be able to Pokemon Platinum, or ANY Pokemon game for that matter.

Find a game that helps her read, then most of the recomendations said.

Girls LOVE simulation games like Harvest Moon and Animal Crossing. Rune Factory is another one. I know because I have a little sister and cousin who like these games.