Maybe jenniy is right.

Not all therapists have the same expertise. She may have said that to someone and they were able to stop.

If she is any good she should be able to suggest someone with more skills in this area, if not, it's good you found out that she's not able to help with this.

You did the right thing to tell her, if she didn't know, there was no chance she could help you address it. It's hard to change, but it could be for the better.

Are there any organisations in your area for people who self harm? They may be able to suggest a therapist who specialises in helping people who want to try to reduce self harm.

I saw someone for a short time, funded by a charity and it really helped, though I'm not cured yet, I have more chance to kick the habit.

Whatever you do from here, the best of luck and I really hope you get the support you need.
❤️