Oh, the poor kiddo! No heartbreak is easy, but I'm of the opinion that the early ones are the toughest.
If it's any consolation, let her know that when a "young" relationship ends, a true romance may be just around the corner. At 18 the "love of my life" dumped me. 4 months later I met my husband, we were married shortly after I turned 19, and this November it'll be 10 years of happiness.
As for managing and uplifting her spirits, I can suggest what my daddy always did for me when I had a heartbreak.
My dad was a colonel in the air force, and while he was 100% military man, he is also one of the most gentle and kind men I've ever known. Whenever he'd get home from work and find out from mom that I was in my room sobbing from a breakup, he'd knock ever so gently on the door, come sit beside me on my bed and put his arm around me. Once my sobbing settled enough that I'd be able to hear him, he'd say in his deep voice, completely seriously, "You want me to get out my service weapon?"
We both knew he wasn't really offering that. But just knowing that my dad was 100% in my corner would help me to see things a little brighter. Plus, not only was he telling me in a very non-confrontational way that he thought I deserved better, but he wasn't trash talking the boy. That way if we ever did rekindle anything, dad wasn't a 'bad guy' for having tried to cheer me up.
Perhaps your husband could try something along those lines? Also, from one mommy's girl who is still a student to a student's mommy, don't stress too much about her grades. It's early enough in the term that she can pull herself back onto the rails. But when things get rough for me outside of school, and my parents immediately jump on me to "not relax my educational efforts" it makes me bonkers.
If all else fails, it may be time to step out of the mommy shoes and into the girlfriend shoes. Rent some man-bashing movies, stock up some horribly bad for you snacks, and dish about all the cruddy gents you dated before you met her daddy.