oomis,
I agree with the ideas expressed in your post, but I will nitpick on one detail. I think a favor is a chessed, although someone has a right to choose how far to go with a chessed, it’s still a chessed. (we’re probably just using different terminology to express the same idea). In the particular scenario in this thread, I fully agree with the OP, you, and other posters that the girl had an obligation to do her chessed in the way it was originally arranged, and it was wrong to inconvenience the recipient of the chessed the way she did.