How about confronting them about why they're ignoring you? If you honestly can't say that you did something to upset your partner, and it was completely unexpected, then a direct approach is probably the best way to go about it.
If the relationship's that important to you, then find out what's bothering her, and fix it. If you can't fix it, then work around it. If you want the relationship to work that badly, then chances are, you'll make it work, somehow. I believe that your friend wasn't too into the relationship. Otherwise, he would've been determined to find a solution.
If the girl didn't want the relationship, and was ignoring her partner so he'd get the message, then congrats to her. He got the message.