What do you hope to gain from telling her? What you describe rings alarm bells and you need to tread carefully here. Attraction often emerges in therapy and it can be useful to talk about, but both parties need to be clear on where the boundaries lie so the feelings can be discussed openly without exploitation. If you want to tell her as a way to understand and work with these feelings and where they're coming from it might be useful, but acting them out in the relationship isn't ethical. My suggestion is to be honest with yourself about why you want to tell her about your feelings and reactions. If it's because deep down you're hoping she might feel an attraction to you, that's definitely a sign to slow down and consider what you're in therapy for. If your therapist shows any signs of attraction to you that's a definite indication you need to find a different therapist who keeps ethical boundaries. And self-responsibility is a factor here too in knowing what brings this reaction on and how to prevent it disrupting your therapy work.