Quoted from EvanDickson:I'd say without throwing the game, change your personal goal to something besides max points. Focus your game on getting to a tough challenge, or max number of loops or something. That way you'll still have a challenge for yourself, you're not throwing the game, but your gf may have an improved chance to beat you score-wise.
This is the approach I like to take especially with novices playing at home. Offers me a chance to work on my trick shots without running up the score on them. I also encourage them to shoot first just so it gives me the opportunity, if they have a big lead, before playing my last ball to ask them, " we could quit now and call it a tie", And then bring the heat. 
