My granddaughter has had four severe nosebleeds in two days. She is 10 and has had them about once a year the last few years. What could this be?

Most likely: fingers. Agreed with dr. Ho. Also: nose bleeds (epistaxis) is most common this time of year - toward the end of the cold-and-flu season, and end of winter when we have lived with forced-air heat for awhile. Inflammation ('colds', allergies, tobacco smoke, etc) of the nasal lining will increase the risk of bleeds. Plz take a look at my med-ed site (boogordoctor.Com) for several articles on this topic.
Many causes. A few small nosebleeds each year is ok.. The most common cause of nosebleeds in children is due to nose picking/ trauma. Other common causes include mucosal dryness, foreign body, and allergic or infectious rhinitis. Bleeding disorders should be considered if recurrent, prolonged nosebleed. You can try a humidifier, nasal saline spray or vasoline. If bleeding continues, bring her to pediatrician.