Instead of saying "My therapist says", maybe you can say, "I think you are..." As in, "I think you are minimizing my feelings." Or better yet, "I don't want to talk about this anymore because you aren't really helping me feel better."

I agree with you that you shouldn't be using your therapist in your arguments like that. Even the most gracious person would have a hard time hearing "My therapists says you do so-and-so!" and not getting defensive.