I'm like 99% sure she just got that girl to pass out by the pool so she wouldn't die on the roof. I'm guessing Satsuki did it in a scary way because she didn't want to let her go freely, so she wanted to maybe make her stop bullying? I'm a little worried because if Satsuki pulled a knife on her, she'd probably get suspended at the very least so she won't be able to protect her gf... With the way they set up the rumors about Satsuki, I'm pretty sure her actions are just being misunderstood. Cause a ruckus at the sports event? Probably to delay a student from getting to the place where they would die. Push a kid? Maybe he was about to get hit by a car. Who knows though, I could be wrong and we have a big yandere on our hands