OP, I can hardly believe their cheek!
If I was you I'd have to call them out on it. Something along these lines:
"Dear Margaret, I appreciate you making the effort to travel to visit me on Saturday. It was good to catch up.
I told you beforehand that I was not able to cater for you and I assumed that you might have understood how much I would have enjoyed someone bringing lunch for me. I was surprised that you brought food only for yourselves, and then ate it, without sharing, when all I could manage to make was a piece of toast.
During your visit you would have observed how incapacitated I am at the moment. You did nothing to assist me, and then left me to clear up your dishes. As a consequence your visit left me feeling more depleted than before you came.
I understand that it can be awkward in someone else's house, not wanting to overstep and clear up - but you could have asked. You could have asked if I'd like to share some of your delicious looking food. You could have asked if I'd like some help to make my toast. You could have asked if you could make things easier by washing up and putting away the dishes.
I send this because you may wish, in other situations, to be more reflective about how you support a friend in a challenging situation."