Easy check - set the butt of the rifle in the bend of her elbow, her finger should comfortably reach the trigger - if the length of pull is too short, she'll have to bend her wrist and compact her hand/fingers to reach the trigger. On a full size rifle, to see if it's too long, then her hand won't comfortably reach the pistol grip or neck of the stock, and her finger won't reach the trigger.

Big Uncle's point about the scope positioning is also valid - front to back, as well as height above bore. As her face has grown, her eye might be getting taller, so getting under the scope might be difficult.