I had to hang up on my mother in the middle of talking to her because I was just repeating myself, and I just felt like a bratty teen for doing it

Oh no, LW, you were the responsible adult here. Your mother was the bratty teen in this conversation. And if Mom tries to pull the same stunt again despite LW's manager's warning, then push that nuclear button and call CPS.

Mom should count herself lucky that LW's manager did not call the police after Brother was caught on tape harassing LW's co-worker.