Tempted to put this in almost heart-warming because logically speaking, she completely forgot about said promise up until this very moment.

KillRoB-XV said:

Tempted to put this in almost heart-warming because logically speaking, she completely forgot about said promise up until this very moment.

Well, I think it's implied that she's been taking care of Youmu as promised. She just didn't tell Youmu about the promise, partly because she never knew how Youmu felt about Youki and thus didn't realize it was necessary.