To say that Granny didn't repay him, I think is wrong. She repaid him with the only currency she deals in - respect.
At the beginning, Oats was objectionable, wet, naive, and derided for his beliefs. Because of Granny, he grew up as a person and he became respected. All the people went to his service at the end because of what he had done for Granny. Granny herself, doesn't want thanks for all the times she helps people, she only wants respect.
Granny wants people to work things out for themselves. Oats should have been able to work out for himself that Granny appreciated his help.
And also she couldn't go to the service at the end for two reasons;
Firstly she was knackered after having nearly died the day before.
Secondly as a mark of respect, she didn't want to steal the spotlight from Oats.
PS I did say that Nanny accidently
gave Granny the plan about the blood.
I didn’t want to take the time to point out how wrong you are from the book, but Granny doesn’t give him respect herself. She doesn’t do anything but smile at him when nobody else is around. The respect shown by the people of Lancre may have been generated by Granny, or approved by Granny, but it has very little to do with the change in Oats. When Nanny tells him there are a hundred, maybe a hundred and fifty people waiting for his service, Oats thinks:
“Levers, thought Oats, and had a fleeting vision of the pictures in Nanny’s parlor. She controls the levers of lots of people. But someone pulled her lever first.”
That Granny wants something more in return than respect is intertwined with the intensely painful passage beginning with “Choices. It was always choices.” She goes on to think towards the end of this long passage:
“She’d never asked for anything in return. And the trouble with not asking for anything in return was that sometimes you didn’t get it.”
I don’t think there’s any support in the witch novels for your statement that Granny wants people to work things out for themselves—witches perhaps, but not people who are not witches.
As to the last two statements about why she doesn’t attend—they are (as I originally intended to say) pure nonsense. Granny has slept all the way home, snoring to beat the band. There’s no reason to think that she’s “knackered” the next day. And had Granny attended the service, it would indeed have shown respect for Oats—to other people. Instead, she chooses to borrow as an eagle—and later that night as an owl. She thinks of what she wants to do.
Granny cannot allow anyone to “beat” her—and for her that includes admitting that she needed help. Oates doesn’t feel bad about her failure to thank him. He thanks her for what she’s done for him. And he goes off to bring light into the darkness of Uberwald without discussing the matter with her.
There is no contradiction in what I said. Terry makes Granny fallible, which is brilliant writing. I just said that I wished she’d thanked him.