woman who threatened my sister works at my pediatricians office

what should I do? when my sister started dating her now ex his ex wife tried to make her life hell. she called/text her from several numbers and left threatening messages, saying she knew where she and her daughter lived and didn't care what happened to her, etc etc. that sort of crazy nonsense. my sister is actually at court right now dealing with this crap and we just found out the bitch works at the our kid's pediatrician's office! I have fb messages from when I told her to leave my sister alone and she responded, admitting to what she did. I want to take this to that dr office. she is unstable and will do anything when she's angry. my sister had to get a restraining order and now she works where my niece and my daughter go to the dr. what can I do? she could lose her job anyway but I don't want to wait, I want her employer to know what sort of psycho they've got taking kids temperatures. can I just go to the office and show them the convo? I do not want her around my daughter and niece.