I also once thought I needed to “help“ the girls I liked. And by that I mean trying to talk them into making decisions that I liked.
But the fact is that all you can do - the only right thing you can do - is telling the truth, and that's it. For example, if her boyfriend threatened you when she wasn't around, just tell her that. And THAT'S IT. Don't scheme, don't persuade, don't lie. Tell her ONCE and move on. Respect her decisions.
In the case you described above, you could have asked her if she really thought that he was the right guy for her. Once. And if she needed help that you'd be around. Again, say that once and then move on. If she agrees with you, that's all you needed to say. If she doesn't agree, then persuasion won't make any difference.
My advice for you would be:
- stop using Facebook and other social media that much
- stop making up these conspiracy stories. Take things for what they are: plain and simple
- learn to tackle things in a direcf fashion: either ask someone out or move on, for example