Wow, I would be super mad about T giving an appointment time to a friend. I mean, it would have been bad if you found out that you had to lose your spot to someone else in the first place. I mean, if your T was rescheduling people, why did she take the time away from a a regularly scheduled client?

Wouldn't the people in the time slot where she'd be away need to take the hit? Unless someone was like suicidal of course....

I agree that you need to separate yourself from this friend or enforce stricter boundaries. If you can't be honest with your therapist about your life, then it's sort of pointless to see her. You certainly don't owe your friend any favours.