Interesting question. I have only had female T:s and I´m a female myself considering myself heterosexual but I still have felt a kind of attraction to some of my therapists. First there has to be a connection when I often idealize the T and then I can find her attractive in nice clothes or by how she moves in her office for example. I don´t get excited but more like it´s forbidden to see "too much" of her breasts and that has happened in situations like when the T leans forward wearing a low cut top or similar.
I find it attractive when a T is 50+ or 60+ in age and still has a nice figure, nice clothes and it´s then inevitable to not at any time glance at her breasts. It´s not that I stare and I feel a bit embarrassed when I happen to look there but I´m sure they do to, like when a client enters their room and from a distance you don´t see exactly where your T put his/her eyes. I don´t desire those T:s but instead the erotic thoughts or erotic transference makes me think of them and their possible sex life, if they have an active sex life, with whom, how often and so on.