Maybe you could make a list of words that you associate with what happened, and you might get some relief from telling her these words? You wouldn't be saying what it was, but you'd be describing it indirectly. Any words at all, whether emotions or adjectives or items in the room -- even "broccoli" if that was on the table -- just anything your brain connects to this event? Maybe if you talk around it, some precise words about exactly what happened will slip out too.

And just know you are not alone in this, so many people here have described the agony of trying to get something out while in session.