That seems too often for such a young child...But it also might be nothing. Easiest thing might be to have the school nurse check her vision. I checked the Mayo Clinic and they said kids do get headaches but they are often just "different" than adult headaches:
Migraines
A migraine in an adult almost always affects just one side of the head, whereas a child's migraine often affects both sides of the head. Also, migraines in children typically don't last as long.
Tension
Often, stress related, tension-type headaches feature a pressing tightness that occurs on both sides of the head. They can last from 30 minutes to several days.
Chronic
Both migraines and tension-type headaches can begin happening more frequently. If your child has headaches more than 15 days a month for more than three months, doctors call this a "chronic daily headache." This problem can occur when your child takes pain medications — even the nonprescription variety — too frequently.
Cluster
This is the least common type of headache in children. It's usually disabling and involves a sharp, stabbing pain on one side of the head that lasts less than three hours.
Mayo says a child should see a doctor when headaches are reported more that 1/month, when they have followed and injury or illness, when they trigger vomiting, dizziness, or vision issues, or when they come with fever or neck pain