I'm not sure you can really tell a T "too much," as their job is to help us deal with all our issues and past traumas, big or small. Does it help to tease apart what exactly you're afraid of? If you're worried she will think you're gross or disgusting, that concern is coming from the trauma itself and the way it's made you feel all this time... but she's not going to feel that way. She might be disgusted at your grandfather, for instance, but that's totally separate from caring about you. Are you worried about surprising her, when she thought things were fine? I think that instead, she would just think "Oh wow, I'm really glad she's letting me in now, and sharing these things."

I'm sorry you're suffering so much with this!