For me, believing things that I cannot possibly know to be true (like what's up with another person) is always wrong. I focus on trying to figure out what's true for me, which is why I find disappointment so hard and take things so personally when someone does something to slight me. Keeping in the forefront of my mind that what people do has mostly to do with them, not me, this is what I think of your possibilities.

1. Sincerely doubt this, and you can't possibly know what she remembers and has forgotten. But does your diagnosis mean she should have called the other client, canceled the appointment the receptionist gave to them, and given it to you? I can't see how one thing leads to the other.

2. Same. You might want to consider challenging your own belief that your diagnosis, or even just being you, means other people have to respond to you in particular ways.

3. "This" is the fact that she didn't give you an appointment that was already schedule for another person? I don't see how she would have offered it if she knew it was already scheduled for another person. That just seems like miscommunication between the receptionist and herself. If the receptionist had told her that appointment was booked, she wouldn't have offered it to you and then you would be back where you were, apparently not needing next week's appointment. It's a classic to say that people don't care when they don't do what you want, but that's also a belief worth challenging yourself about. And just like #1 and #2, your interpretations are all about the other person, whose mind you can't know unless you ask them if these things are true.

4. Maybe she is "right," except in the story you told, she didn't do it.
Why do you assume it's because you are "bad" and the other client must be better? That also seems an interpretation worth exploring. I don't know too many therapy clients that haven't had trouble with some scheduling. I've canceled an appointment or two and then asked for it back, sometimes I've gotten it and sometimes it was already given away, but I'm the same. Taking it so personally, using this kind of random mistake as a way to beat yourself up, maybe that is one thing you could let go. It's fine to be angry or upset or whatever at the T or receptionist, I don't really care and I think they can take it just fine, but it's the self hating interpretations that are really hard to listen to.