Ok op I will give you serious advice (You are going to need a gun, a suppressor is also recommended btw should be easy if you live in cuck states)
-Follow her for a few weeks (Obviously stealthily), follow her learn her schedule, boyfriends house, her house, places she often goes too etc You are looking for the most secluded area which she visits, should be at night time too.
- After watching her for a while, by now you should know her movements very well, you should also decide when you are going to kill her.
- After you have decided wait till night and till she visits you chosen spot, make sure you have some sort of face covering on (A mask or something like it) as well as all black clothing, gloves are recommended, a car is also recommended, although if your location is secluded enough you won't need one, check your gun is loaded and safety off, all good? Ok now you walk up behind her put the gun to her head and pull the trigger, slip your gun away and walk back to car (if you used one) or the other direction of the body for a long while.
- Once you walk or drive to what you gauge to be a safe distance you are going to want to dispose of your clothes (Burning preferably, I should of also said earlier to bring a different pair for changing into)) and the weapon (throwing it in some sort of river or reservoir) obviously far from where you killed her, one city over is great, two if you want to be extra safe.
After this I am sure she will not bother you again and you should be fine in terms of the law. Should be.
(Of course this is all a joke I could never incite or promote any kind of violence That would be terrible and I am an upstanding moral christian, so could never do such a thing)