I read Tisarwat as a 17yo who doesn't know who she was, but does know what she is now. I'm not convinced all of Tisarwat is gone - her childhood built the brain structure AM's download is now running on, but her original personality* may entirely be (c.f. the scene in AJ with replacing 1 Esk's dead ancillary when they are ordered back to JoT and the comments about horrified reactions from the newly awakened ancillary, some of which never go away - though that may just be typical Radchaai ruthlessness, easier to decant another body and start again than actually understand what is happening).

* 'personality' gets complicated here, because we normally think of personality as the sum of life experiences plus (for want of a better word) nature. AM has dumped in life experience, but I'm not sure nature will have been so thoroughly targetted, plus Tisarwat is still physically a 17yo, with likely implications for emotional stability.