If your therapist were to be angry at you, for telling her something that distresses you, then she would be pretty useless, in my opinion. I'd tell her; you guys don't have to work on it, but simply telling her and getting a quick view on it, might help you a bit.

I imagine there's some sort of history that links you to this obsession with paper-cuts.

That would maybe hurt me if a partner were to tell me that, albeit probably gradually, and quietly. Sometimes I tell myself that, but when someone else says it to you, particularly at a vulnerable time, it can sting a bit, or at least, that's how it goes for me.