Oh jesus. Are you playing against her right now? Or can you train for like 1 hour? There is a training mode that you should go through.
Otherwise, here's the deal: play conservative on offense, don't go for big home plays, just go for short ball control style plays. Look for routes where your receive cuts back to the ball or cuts to the sidelines, and hit the pass button on those cuts. Use runs up the middle and just plow forward... You won't break a long touchdown, but you'll be fine. Punt the ball on 4th down, play smart, play field control in the first half.
On defense, for teh first half, play conservatively. Use lots of zone defensive plays like the Cover 3, Cover 6, and Cover 2. These are basic zone defenses. I'd wager your girlfriend is likely to pass more than run so you should assume most plays are going to be a pass. These defenses will do an adequate job of defending. Now, after the half, change up your gameplan on defense. Still pick zone defensive plays but start calling lots of blitzes on 1st and 3rd down. This will frustrate her. She'll be expecting conservative 4 man rushes like in the first half, and then suddenly, her timing will be all off as you'll be bringing guys from every angle. She'll give up sacks, make mistakes, and probably quit the game in the 3rd quarter after you get two interception returns for touchdowns.
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