I'm so sorry to hear that. I'm 26 and in a very similar situation (age, at home, mom as contact, self injurer) but I have absolutely no idea why she would feel the need to tell your mother, nor do I think it was 'serious of a situation enough' for her to suggest it. Is she a fairly new T? Has she dealt with self injury before?

Did you mean that she actually said that at the actual first session? Honestly, this may not be the best advice, but I don't actually think I would be able to trust her after said threat and would find another T whose idea's of therapy were more similar to the type that could help me.

My T tells me all the time the she knows that self harm is not the same as being suicidal. I went for months not telling her things of that nature despite her asking and it wasn't until we had a heart to heart break it down to specifics on what I would have to do/say to be admitted before I really began to open up to her. Perhaps you should address with T her views on self injury, suicidal ideation, the mental health system, admittance to hospitals etc. before offering any more information and then decide if she is, indeed, the right T for you?

I would caution you to be weary as she seems to be a bit irrational, imo.