请根据以下短文内容，回答短文后面的问题，答题词数不得超过10个单词。
Many years ago,my dad worked in a children's hospital.A girl in the hospital had a strange illness.She couldn't move her hands or feet.She could only move her head.She lay on bed every day and she was very sad. Even the doctors couldn't help her.
My dad decided to try his best to help her.He brought paints,brushes and paper to her room.He hung(悬挂)the paper on the wall,put the brush in his mouth and began to paint.He didn't use his hands at all.Only his head moved.My dad told the girl,“See,you can do anything you want to.”
Soon the girl began to paint using her own mouth.She and my dad became good friends,but my dad fell ill at that time and he had to stay at home.
Three months later,my dad went back to the children's hospital.When he went into the hospital,the girl ran to him and hugged him tightly.She gave my dad a picture and said,“I drew this picture with my hands.Thank you for helping me.”
My dad would cry every time he told us this story.He would say,“Sometimes love is more powerful than doctors.”
1. Why did the girl give the writer's father a picture?
