I would not make any hard and fast rules before you enter a new experience. Tell the therapist what you want to tell her; why you are entering therapy at this time, what you see as your biggest problems, etc. Your symptoms aren't going to go anywhere right away, you want and need them and are doing the best you can to cope with your anxiety, etc. It's not like you tell a T everything in the first hour and then you're done. Get a feel for how well you like her and if you feel you can work with her. There's no point in telling someone something only to find they were the "wrong" person to tell.