Not Able to Change sprite when animation running

Hi I am new to Unity and stuck at a problem .

Here is my enemy.cs file

    public class enemy : MonoBehaviour {
 private Animator animator;

 void Start() {
     animator = GetComponent<Animator> ();
 }

 void OnTriggerEnter2D(Collider2D collider) {
     if (!animator.GetBool ("IsEnemyAlive")) {
         return;
     }
             // Do something
 }

 void Update () {

     // Base Condition
     if (gameObject == null) {
         return;
     }
           // Do something.
 }

}

Here is EnemyGenerator.cs

  public class EnemyGenerator : MonoBehaviour {
 public GameObject enemyPrefab;
 public Sprite[] allEnemySprites;
 private float[] allEnemyHealth = {100f, 150f, 200f, 250f};

 // Use this for initialization
 void Start () {
     generateEnemy ();
 }

 void generateEnemy () {
     foreach (Transform child in transform) {
         GameObject enemy = Instantiate (enemyPrefab, child.transform.position, Quaternion.identity) as GameObject;

         // Change sprites and Health
         int totalSprites = allEnemySprites.Length;
         int randomPosition = Random.Range (0, totalSprites);
         enemy.GetComponent<enemy> ().health = allEnemyHealth [randomPosition];
                     enemy.GetComponent<SpriteRenderer>().sprite = allEnemySprites[randomPosition];
     }
 }
 
 // Update is called once per frame
 void Update () {
     if (AllEnemyDead ()) {
         generateEnemy ();
     }
 }

 private bool AllEnemyDead () {
     foreach (Transform child in transform) {
         if (child.childCount > 0) {
             return false;
         }
     }
     return true;
 }

}

And here is my state Machine

Entry ----> EnemyAnimation -----> Idle -------[IsEnemyAlive] -----> EnemyExplosion -----> Die Now here EnemyAnimation is Default state so it run everytime when a enemy created and idle state is a loop to keep enemy in correct position.

When I am trying to update sprite in EnemyGeneration method but still it is showing default sprite in game mode and health is updating. Please help me and sorry for bad english