Wow..an ultimatum. An all or nothing approach...I see where your T is coming from, but at the same time to just give someone an all or nothing approach doesn't seem like the a good therapeutic approach to help anyone stop from hurting themselves. Especially if it is something you have done for years. I have bulimia..understandably not the same as cutting at all..but my T is helping me through it and we are working on different coping mechanisms and we talk about my ED and she usually starts out the session with asking how many times I have binged/purged, purged, and used laxatives since our last session. She has never told me to basically stop or I can't see her anymore..that would send me into a deeper downward spiral like no other. I can't tell you if your T is wrong or right..I can only go from how it seems from my pov. Maybe try bringing in whatever you use to self harm with and talking about how her ultimatum made you feel and what you think.

Truthfully you could just throw your self harm object away and follow her ultimatum, but that won't stop you from self harming because you can always get another object.