Maybe I'm being a big derp and/or reading too much into things but, what was the significance of her taking the receipt?
I guess maybe to learn more about what her sister likes to eat while not at home? Very clear the kinda person she is, wouldn't put it passed her. To pay for their order herself? I can't immediately think of any other reasons.
Am also thinking that last page about the "Kuon she hates" disappearing is more about possibly abandoning her career as a singer-songwriter than performing a quintuple flip.