Sorry you had such a bad experience with this person, it is definitely something to do with being a minor but I don't agree they should treat you differently.

I had a similar experience when I was 13, I was seeing a counsellor for 12 weeks and then that counsellor got replaced with another because I wasn't doing 'well enough'..the new one invited my mother in to the room and started talking about the abuse and self harm like it was nothing. My mother didn't want to hear about that either. I never went back to her, I became much worse and didn't seek proper therapy until I was in my mid twenties because of it. Don't let this persons ignorance affect you, they clearly don't understand what you need. You deserve much better.