I understand your stress. It was utterly painful when I expressed my transference to my T, but she accepted it very warmly. You already have a good solid working relationship with her so trust that and use that as a resource to build up the courage when you do talk to her. Think about her warmth and what you know to be true about her in her past dealing with you. And as AG would say "BREATHE."
If you haven't already done so I find it helps to write out my feelings on paper to try to get a clear idea of what I want to say. Then if you're like me you will probably stumble around it anyway.
Some of us write letters or emails to our T so they can read it before hand and then it's already on the table when you show up. You can even just present the letter to her in person and let her read it and then discuss it. I've done this on difficult issues too and I find it really helps. I have learned that there isn't anything I can't discuss with my T. It doesn't mean it's easy, but it's true. If this is distressing you too much to disclose this to her, just take it slow. You can at least relate that there is something distressing you that you need to discuss with her but don't quite know to go about it. She may help ease it out of you or you may be inclined to say "I'm just not ready yet." But take it slow and try to feel as grounded as you can.
Take care!
JM