That'd be a little difficult as I think the controller itself might be hard for her to play with... I know many of my friends even gf sometimes has a hard time with the controller. Has she played with the controller before?
There are games like the lego racing(forgot the exact name), fusion frenzy, and I think something like barbie horse adventures which are all pretty basic. However, I don't think lego racing or barbie horse adventures are all that great, and seem really poorly made(never played barbie games on xbox but have tried one once on playstation just to see what it was like and it was bad).
I'd say your best bet would be to get some emulators and put some old simple games on there for her to play with. Mostly platform games seem like the most fun for girls(sorry if i'm generalizing, but its what i've noticed from my experience).
If she can't really get the hang of the controller, you might want to buy an old SNES or other old console with much fewer buttons so that she can learn easier.
I remember when I was 3 I was playing on the atari and my dad had bought a commodor 64 where the joystick had only one button. Of course times are changing and kids are growing up faster than before.
Hope this helped some
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