I think it's safe to assume that it's not just because she accomplished her goal, considering she admits that the watch has been acting up for a while now. Don't think the author would have brought those malfunctions up out of nowhere if they weren't relevant.Not sure if the watch really is broken due to how much it had been used/rewound, but I think it can be because Yotsuha has finally done what she needed to do; Stop MC Uichi from commiting suicide.
What kind of drugs are you abusing?She's a fucking lunatic who stole the mom's antidepressants and drove her into a mental institution. He deserves her, because what the hell has he done to get the reader's admiration. Too many people here are cheering them on because there's a big MALE LEAD and FEMALE ROMANTIC LEAD sign hung over the characters, but their actual personalities are, obviously, trash.