Unity 2D Shooter - Arm Rotation - unity3d

Question

I'm making a 2D platformer game where the player has an arm that points towards the mouse cursor. This mechanism is used to aim the player's weapon. However, I am experiencing some glitches when rotating the arm.
I know the reason why I am getting these errors: The arm (in the hierarchy) is a child of the player, and what I'm doing to the player is flipping (inverting) its transform.localScale.x value whenever it moves in a specified direction, so that the player sprite looks in the given direction. Since the arm is a child of the player, its own transform is flipped as well, making it look in the same direction as the player, which is what I want. However, this causes some errors with the arm rotation. Since the arm's transform.localScale.x value is flipped, the rotation is all messed up, and I can't figure out how to solve it.
Here are some example scripts for moving the player and arm. They are simplified so that you can read it better.
// Update is called once per frame
void Update () {
var input = Input.GetAxis("Horizontal");
if(input > 0) {
if(!facingRight) {
ChangeOrientation(gameObject, new Vector3(-1,1,1));
facingRight = !facingRight;
}
}
if(input < 0) {
if(facingRight) {
ChangeOrientation(gameObject, new Vector3(-1,1,1));
facingRight = !facingRight;
}
}
rbody.velocity = new Vector2(speed * input, rbody.velocity.y);
}
public static void ChangeOrientation (GameObject g, Vector3 changeBy) {
var newTransform = g.transform.localScale;
newTransform.x *= changeBy.x;
newTransform.y *= changeBy.y;
newTransform.z *= changeBy.x;
g.transform.localScale = newTransform;
}
And my arm rotation script:
void Update () {
//rotation
Vector3 mousePos = Input.mousePosition;
mousePos.z = 0;
Vector3 objectPos = Camera.main.WorldToScreenPoint (transform.position);
mousePos.x = mousePos.x - objectPos.x;
mousePos.y = mousePos.y - objectPos.y;
float angle = Mathf.Atan2(mousePos.y, mousePos.x) * Mathf.Rad2Deg;
transform.rotation = Quaternion.Euler(new Vector3(0, 0,
(PlayerRunMovementController.facingRight ? angle : angle )));
}
Thanks for any help you can offer.