See I think it's ok not to answer a question that makes you uncomfortable or that you're not ready for. I think that's one way you can control the intensity, pace and triggeriness (!) of therapy. Also many of us need a place to practice saying no. I think it verges on bullying to tell you that you can't say "I don't know" here. When you're ready, if your therapist has created a safe enough environment and a secure enough connection, you'll get to the things that were previously too hard too talk about. I think discussing something traumatic for eg in an environment where you don't feel safe defeats the purpose of therapy. It's likely to retraumatize you.