There's nothing worse than seeing your friend hurt when she's going through a breakup. If he has been a bastard and broken her heart you need to step your best-friendship up a notch and get her through it. Begin with the absolute essentials, a wine and whine night within 72 hours of the split. It's about more than just listening to her cry. She needs to get mad. Call out all of his bastard antics, no matter how minor, and identify a few key themes. Come back to these salient points throughout the night. Stick the knife in, twist, and repeat.
Next, you need to protect her from herself. Social media means we're all connected these days, it's just not always for the best. Obviously the number one concern is that she will torture herself by checking his page. The danger here is that she will see a tagged photograph of him with an unknown female and descend into a murderous crying fit. If she does engage in this particularly gruesome form of self-injury, you need to be there to pick apart who exactly that bitch is and have your yellow legal pad to hand to list all the ways your friend is better.
The other danger of social media is that your friend could be going about her day, happy out, and suddenly he pops up on her timeline and slams her back into that bad place. The nuclear option is to block him; out of sight out of mind, after all. If social etiquette precludes her from this then she ought to mute his profile. They'll remain friends online, and it doesn't send the same message as blocking, but she can live her life without risking exposure to his BS.
Once you've covered the basics you can move onto the next phase: getting-over-him-but-not-really-getting-over-him. Think girls' night out and encouraging her to shift the face off the next man she sees. It's half fun and games half listening to her sob at 2am. Conversationally, things might get a bit repetitive, but let her vent. The key to this stage, however, is keeping her away from rebound men. That means no exchanging numbers or last names, even if she shags someone. Especially if she shags someone.
Breakups are tough and there's no way you're going to be able to take away her pain. It can be hard watching her go through it all knowing that nothing you do can magically fix everything. But you can help her get through it. Whether it's cathartic rage-crying, or getting her mind off the whole sorry situation long enough to laugh at a dumb joke, your presence is more valuable than you think.