Just to say - it is possible that your T is a committed T and was telling the truth. For example, maybe she was feeling really unwell on that particular day so she shortened your session, cancelled the rest of her day's sessions, and asked a family member or friend to come and collect her because she didn't feel well enough to drive or travel by herself.

Of course it's also possible that she was lying and wanting to see someone (partner?) more than she wanted to work.

I'm just saying that both are possible. It's totally understandable to be really upset by this happening. Therapy can be such a crucial time when we are feeling low and really need help, and it's horrible to have the T cancel or shorten the session at the last minute.
Maybe next time you could tell T your suspicions and how it makes you feel? I think you may be able to tell by her reaction whether or not she was telling the truth.