Mommy, I wish that Grandma would come back to life. I wish I'd get an 'A' in math on my report card. I better make her understand that Grandma has died and never can return. I should give her realistic information and let her know what's possible and impossible. A beautiful part of childhood is that children have wishes every day and these wishes enrich their lives and your life.
Children have a unique and open way of creating dreams and goals.
Second, no matter how impossible the wish sounds to you, in future years she may be able to reach at least a part of this goal. And yes, a child also uses wishes to gain information about what is realistic. But she can accept realistic information only after exploring a whole range of emotions from disappointment to joy. Sometimes this exploration occurs in minutes and sometimes it takes years. That would wonderful wouldn't it.