Why is St. Therese Lisieux called the Little Flower?

She was called the little flower because Love of God as a Father, expressed in childlike simplicity and trust. which means she showed her love for God as a child would so she is called the child of Jesus. And the "little Flower" was just a nickname for her because she was young and delicate
St. Therese of Lisieux loved flowers and often called herself "A lttle Flower of God."