Dear A.,
From what I have read in several books on our bodies' need for water, having hard stools or poops is, usually, an indication that there isn't enough water being consumed.
Each of us, child and adult alike should have half our body weight, pounds converted to ounces in water daily, so if your child weighs 30 pounds (for example), she should have at leasts 15 oz. a day. (Adults, by the way, no matter what they weigh, should have no less than 64 ounces daily)! Also, if child or adult is suffering from any type of respirtory problem, the need for water is higher (2/3 body weight, pounds converted to ounces)!
Additionally, more raw fruits and veggiesand whole grains in her diet should also help. The fiber will push the stool out easier.
Hope all this helps!
Blessings!
J. F.