You’ve already done a good job here. You were clear and direct about your concern, expressed the fear of judgment for having these thoughts, and showed an understanding that the early childhood experience of hurting an animal is often connected to these thoughts. What you are struggling with takes courage, and you seem to be displaying a great deal of it. It was a very brave thing for you to write these feelings down and send it to us here. Now it is time to take it to the next level and bring these issues to the people who can help you at a time when you are in a safe place and are struggling with these concerns.
If it is too difficult for you to speak of these symptoms directly show the psychologist this blog and ask him or her for an opinion about what the person writing the blog could expect. The purpose of doing this would be to allow you to communicate these symptoms through the blog and then use it as a vehicle for discussing your need for treatment.
You are right that finding a way to express this while you are there is essential because it is, as you’ve said, the best bet for treating what’s important.