Long winded rant! advice needed ASAP before I kill someone

Emily Victoria
Long story.  
My brother (almost 18) broke up with his gf (16).  She then got mad and told our parents they had sex and all that... They both got in trouble. 
Now, nearly 2 months later, she is still STALKING him telling him he can't talk to certain people and this and that.  
He has recently started dipping, right? So she's having a fit.  She told our mom that he followed a dipping page on Facebook and ig and tried to get him in trouble for it.  
She will not freaking stop!  She's bugging Me Bc he blocked her so she can't stalk him anymore.  She's playing the victim!  I can't be rude Bc she knows too much about me, enough to get me in trouble.  I seriously need help.  
PRAY PRAY PRAY! 
not for me but for her.  I might kill her, lol.   (Kidding) but she seriously is not stopping.  I've posted about her before but I didn't say he was my brother Bc she had this app and I didn't want her to find out.  I said he was my cousin.  She is not stopping.  Advice?  Please please please help lol