What color light bulb is in your heat lamp? If it is not red, they may have been pecking each other dopue to light at night. A red heat lamp bulb is better for allowing sleep. Heat lamps are very dangerous, though, and many people lose chickens and coops due to fires each year. So if there is a need for one, make sure that the lamp is securely fastened or double fastened with wire, and kept at least 20 inches from the chicken’s heads or any bedding.
Do you know how cold it was last night to need a heat lamp. It was 12 F here last night, and my chickens did fine without a heat lamp. As long as they are inside without a draft directly on them, they should keep warm enough. Just be careful if you use one. A pecked comb may be all that is wrong. It should heal on it’s own, but watch out for others pecking her head.