My only advice is to start her on a story-mode rather that anything online. The highly competitive nature of online gaming coupled with her first time playing and lack of grasp on the controls will probably embarrass and anger her... Don't do it.
Speaking from personal experience as a bit of a late bloomer into the gaming world... Start on less-complicated games. [My first console was a GameCube, we didn't have much money growing up...] I played stuff like Super Mario Sunshine and migrated on up to stuff like MGS and Mass Effect. FPS gameplay is still a bit odd to me, ie, COD, but I'm working at it. >_< Even stuff like Dragon Age with all the talent points and whatnot is still quite overwhelming.
So don't treat her like an invalid, just start on fun and easy stuff and work your way up.