Being you have e-mail contact with T, write to him what you need to talk about and that you REALLY need to be out--that way if you aren't out, he knows you want the session.

You could also compromise with Teen. I've had to do that more than once.
It's a 90 min session. Can you give Teen some time at the end--like the last 30 min or so? That may help to show her you don't want to compete for time, but you need some time and she can also have some.

We see T 2x week and sometimes we set up that one session is for me and the other for someone else.

Just a couple thoughts....