My 8yr old daughter has a nosebleed that come nowhere why is that? She wakes up to it or just playing.

It's common. Nosebleeds are very common. Once a child has a nosebleed, they likely have a scab in the nose that can break or come off allowing bleeding to recur. Bacteria in the nose can delay healing as can repetitive removal of the scab. Use polysporin (bacitracin and polymyxin) in the nose to keep the scab moist and to reduce bacteria. It can take several days or weeks to heal.
Allergies? One of the most common causes of nose bleeds in children is allergies. If her problem is recurrent, consider this as a possible cause. Other causes such as bleeding disorders, trauma, sinusitis or a bleeding blood vesel are much much less likely but to be kept in mind.