I have found therapists react ALOT more positively about my cutting if they know about it BEFORE they have to actually deal with the already sliced arm. It was my not telling my therapists (at that time I hade a mental health therapist and a rape crisis therapist) this was a factor that got me my first hospitalization. They didn't know cutting was a factor and when my rape crisis therapsit saw my arm she called my mental health therapist and the mental health therapist immediately jumped to the conclusion of "she's losing ground if this is starting to happen or she is in active suicide phase" and off to the hospital I went two hours later complete with police escort to the ER, in the ER stripped and full body search and up on the unit within 2 more hours. It took me almost two weeks in there to finally realize all they wanted to her me say was I feel better now no more suicidal thoughts and no I won't do it again. It didn't matter that I knew I wasn't suicidal. They were going by my therapist notes of no known history of cutting so in her mind I was losing ground and had become suicidal. When I got out I explained to the rape crisis therapist cutting was a factor and I wasn't suicidal and Dropped that mental health therapist for another mental health therapist.

Private practice can have more than one therapist working in the same building.

How about if yuo somehow stear the conversation to say having seen a book in a library about various self injury situations and on the inside cover it said the book was not a replacement for therapy and to find out what your states and mental health agencys protocal on self injurious behaviour is contact them. And then tell her/him it got you curious about protocals and what hers was if she had a client that self injured. Its a safe way to do it. libraries always have books laying around on this table and that and people waiting for their turn on computers pick up the nearest one just to pass the time. And then based on the therapist answer you can decide if you are ready to disclose that you are a cutter.

In any case if you are thinking about having her be a part of knowing AFTER you cut the next time then yea I think its time she knew now before it happens, so save any repercussions of her shocked reaction of BOOM I did this now what are you going to do/ what can we do?