Trying to teach GF FPS gaming

[Synapses]

So in our 3 years of our relationship my girlfriend has fallen in love with WoW and other similar MMORPG's, but thats about it from some very novice CS:S.

She has taken an interest in Planetside 2 based on my extreme interest...

What FPS games do you guys think I can start her out on that would not be too difficult but help teach her the basic mechanics of an FPS game such as Planetside 2?

I am thinking BF3 single player on easy or normal, as she does have the concept of point and shoot down, but she really sucks at CS:S online.

Keeping in mind here, she is a bit of a blonde airhead type... I can tell her something and 5 minutes later I can ask her about it and she has that deer in headlights look with a "Huh?".