I too have the same issue I always obsessed over teachers, females bosses and any female in authority. Now t is object of my obsession. I haven't told her because I am not as obsessed over her as I was my last t. We talked about my ex a lot who was older than me and how I am attracted to older women. T thinks it is because my mother never gave me any love or attention so I crave it and look for it in older women. The maternal longing and sometimes I think t looks to fulfill her maternal side with me too. It scares me how close we get sometimes. My t is 100% straight and told me this and I think the reason I don't obsess do much over her is because she is very open with me and tells me loads so I don't fantasise so much about her.
I wish also your t had of acknowledged how hard this was for you to tell her! It sounds to me like she is weary of going there because she is worried she might not know how to deal with it without harming you lots of ts don't have enough training to deal correctly with it. Maybe you should ask her can she help you through it and if not find another t?