I would start with telling her you remember, it is bad, and you are afraid she won't believe you because your mom would not believe you growing up. Then I would just tell her what you remember, how it came about that you remember now, about your body memories, and all of it, just spill it.

I know when I have told T things that were really difficult, the response was often different (but actually "better") than I was expecting. When it is all inside our head and hearts, we have trouble with being able to think about it in any other way and that is what makes telling someone we trust about it helpful I think. They see it from a different perspective and that can often help it not be quite so "everything" like it seems when it is stuck inside us. It's like that "nine dots" problem: Most Wanted Solutions: 9 Dot puzzle