Final answer:
Emma knows she is a girl, which is her gender identity, but lacking the understanding that her gender will not change in the future indicates she has not yet achieved gender constancy.
Step-by-step explanation:
Emma, who is almost 3 years old, has achieved gender identity since she knows that she is a girl. However, the fact that she sometimes says things indicating that she thinks she may become a boy in the future suggests that Emma has not yet achieved gender constancy. Gender constancy is the understanding that one's gender is fixed and will not change over time, which typically develops by age six or seven.