I can understand why you are knotted up over it, but you don’t need to be. You have the control to change the way you feel about canceling. Can you just keep it short and sweet? Dear T, I need to cancel our scheduled session do to finances. I will reschedule when my situation is better. Thanks, Art.

Or..
Dear T,
I need to cancel our next session. I will reschedule at a later date. Thanks, Art.

Done. A few words is all it takes.
Maybe your knotted up because you want to go even though you have other financial responsibilities right now? I’ve fought with those feelings a lot. But I got the courage to just stand up and think for myself:
“No! I need to take care of this other stuff first. If I go when I can’t afford it then it just makes the money situation worse. T might be helping in other ways, but she doesn’t pay the bills and I need to put those first right now.” When I thought of it like that, I was able to feel different about canceling.