Besides the blood on her nose, is she acting fine otherwise? Drinking, eating, breathing O.K? Could you take a picture of her bloody nose? Could you inspect around her body, inside her mouth, and around her pen for any sign of blood?
Chalk is fairly safe since it's used by kids so often, but if you'd like to be precautious, you could try giving her some activated charcoal, molasses, or add Epsom salts to her water to help flush it out of her system.