just my personal interpretation, but based off of how she has to reaffirm herself multiple times about it, she probably wasn't truly happy with her life. i think she was content and fine with how things were, but she also knew that mayumi would always be more "free" than her in a sense, therefore her happiness would always be "truer." it's not that her entire life was a waste, more so that there was just a completely different life she could've lived which may or may not have granted her more fulfillment