My 11yr daughter woke up with a pool of blood in bed from nosebleed bleeding continued for 15 minutes from both nostrils no known cause/other symptoms?

Nose bleed: If that happens again- apply pressure firmly to the nose and bring it up to the pediatrician if it recurs. Dry weather and nose picking are the most common causes of nose bleed in children. However if it continues and other symptoms- fatigue, decrease apetite, weight loss, fever, in addition to nose bleeds- bring her to doctor for further evaluation. Using nasal saline and humidifier may help.

Irritants/allergies: The tiny blood vessels in the nasal membranes will often break & bleed after trauma. Kids will rub the nose when half asleep & often wake to a bloody pillow/bed. Nasal wetting gel (ayr gel) or nasal saline at bedtime can reduce this process.Covering the pillow/bed in allergy encasements can reduce constant exposure to dust mites.