I think your plan seems a good one, especially as it seems to feel right to you - you said you feel calm about the decision you've made. I don't think you need to concern yourself with what your T thinks about it, just get on and do it if you want to. You don't need to explain anything. You could send her a note afterwoods e planning if you wished. Your plan sounds like it puts you in control, which I think is a good thing, therapy can leave us a bit powerless at times I think. When I left T1 I always had the option of going back to do an ending if I wanted, I think that was helpful to me.