Well she is right...the more you give into the thought, the longer it is going to stick around. Here are some book recommendations.
Self-Coaching by Joseph Luciani
Overcoming Obsessive Thoughts by Christine Purdon
Have you talked about possibly taking medication?
Hello there. Glad you are seeing a therapist. One of the first things you should learn from therapy is to recognize an OCD irrational thought and not run with it. You need to learn how to calm yourself down and self-coach yourself through the situation. You know you didn't get pricked with a needle...deep down you know it. You need to think the thought, counter it with some self-coaching, and then let it go. If you continue to do the "what-if" thing with it, then you are going to drive yourself crazy and the thought isn't going to go away.
What techniques have you learned so far to help yourself in these situations?