Allow her to have a day of mourning, then get her out of the house and keep her busy. I had mine doing all sorts of things for a couple of weeks (from sports, shopping, movies, etc), and as much as she hated it (and probably hated me at the time for making her do these things), she admitted that it was the best thing in the world for her. By the sixth day, she started to smile again (without tears), a few days later, she started laughing again. She also returned phone calls to friends she had neglected because of being with this guy, and is now having the time of her life. She has even started to like a couple of other guys that have shown a bit of interest towards her.
Oh, and one other thing, seeing that we're all here because we all obviously are overweight or maintaining- one thing I didn't let her do, was over indulge in food. Instead of buying her that chocolate to feel better like our Mom's might have done, I bought her a notepad and pen, to write down her feelings. I told her to tear it up after she wrote her feelings down if she wished, when she was done. When she was feeling angry, I told her to take it out on the stationary bike, lol. In other words, I don't want her picking up the bad habit that I have- eating when I am hurt, scared, or stressed out. It would have been so easy to buy her her favorite Snickers chocolate cake and down it with her, but I felt that the best way for her to get over this was in a healthy, busy manner. Heck, do a craft with her, anything to keep her mind off her pain and busy.
Hugs to you and your daughter. I hope she will be ok soon, it is so heartbreaking watching our kids go through this pain!