Your partner does not want to improve her defense? When I train with a partner, we'll do exercises for both of us, but always the same one, switching in between sets. This has multiple advantages: While you're resting (in this case throwing / attacking), your brain has time to process how to do the shot, so the second and third sets are often significantly better. Both partners can look at each other's technique and learn from it correct it. There's no discussion about fairness - we both have about the same training.