You are never a disappointment! Nor are you a failure. If you think that, then all things you try make you worthless. Which is far from the truth.
You tried. That is wonderful progress. As with anything worthwhile, trying is the key. The point here is that you made the effort. You did tell your therapist about your desire to talk about the assault. And I believe she is right. There are many people who write out their thoughts and feelings better than they say them. There is nothing wrong with that. It is all about what works best for you. You are trying to communicate and however you are best at doing that is the way you should do it.
You are not going to be able to talk about something as horrible as an assault without feeling anything about it. That is unreasonable and nearly impossible. If you were that out of touch with your feelings about the assault, then you would need therapy to help you through it. The best thing you can do is feel those feelings. That is what helps you heal.