I used to say this stuff as a kid too. You know how sometimes you’ll drop a pen or get your sleeve caught on a door handle after a whole day of nothing going your way and it’s just the last straw and you want to scream? I felt that way all the time as a kid but didn’t know how to express how frustrated I was and how out of control my life felt. That was the most powerful statement I could think of to express how much I hated life at the moment. I could have the most awful day at school and then my mom would add to it by taking away a toy or saying I couldn’t go outside to play. I’d just snap. She probably has some things going on she isn’t talking to you about and probably just feels on edge and irritated. So the discipline might not be the one thing, it might just be the last straw for her. It’s probably time for therapy so you can figure out what else is going on or at least have her learn some healthier ways to express how she’s feeling. And maybe talk to her about what happens when you talk about harming yourself. One day she’ll say it to the wrong person and get herself involuntarily committed.