How unfortunate that we come to a therapist with a history of trust betrayed and instead of finding healing via a corrective emotional experience with the therapist, we are once again betrayed.... what a shame.....
I might consider calling therapist a.s.a.p. and ask her why she left that message, and does she recall being asked not to leave confidential messages? And advising her not to leave any messages in the future. The most she may do is leave a message for you to call her back. How's that?