I once put two eggs from a non-broody chicken under a broody one. I went out in the morning 21 days later, and fond one hatched and the other hatching. The one that had hatched looked similar to yours, but worse. I made the decision to remove it so I went and got a towel (you aren't supposed to touch them till they are 10 hours old) and when I came back the mom had thrown it out of the nest and it died. I put the mom in the yard and put a heat lamp on the egg till it hatched. That chick survived. Chickens live by the "survival of the fittest" rule. If there is a weak one, then they kill it to ensure that the strong ones that can reproduce survive long enough to do so. Because of this, if there is blood chickens then all gang up on that bird to kill it. The mom probably started out trying to clean it but it started to bleed so her natural instincts to kill kicked in. It dose not mean that your hen is aggressive, any chicken would do it. Your chick should be kept warm and should be watched and monitored closely. Chickens are resilient, so she should be fine.
