I'm not sure what you were looking for in terms of a response to this post. But I noticed you had yet to receive a reply. So I thought I would write one. (I do recall reading your introductory post on the subject.)

Your title asked if BDSM & PTSD "mix". I don't know what you mean by "mix". Certainly if a person (a child in your case) were to be subjected to repeated episodes of sexual assault, over an extended period of time, this could cause the person to develop complex PTSD I would presume. I'm not a mental health professional though. So that's just my personal opinion.