To my understanding, a portion of beak this large may not grow back.
If you don't want to cull this chicken (which may end up being the most humane thing to do...) it may be worth a try to glue the beak back together. I know that sounds crazy, but there are cases where that has worked to at least lengthen a chicken's life. I would try super glue of some sort - preferably with low fumes if available. Do it as soon as you can, gluing the hard part sticking up to what is left of the base of the hard part at the bridge of the nose.
I suppose if the hen is lost anyway, it doesn't hurt to try glue.
Even if the beak can not be repaired, if you're willing to have a "special needs" chicken, she could be fed soft mash once she's comfortable enough to eat.
This one is a toughie, and ultimately it will be your call. It will depend on if the chicken is in pain and how much you're willing to do for her... possibly for the rest of her life.
Keep us posted...