When we first meet Juliet, she is about to turn 14. As a child, Juliet is very obedient. This is seen in how she responds to her mother's calls immediately. When her mother tells her about Paris' party, as well as the fact that Paris is interested in her, Juliet tells her mother that she will only go as far as her mother allows her. This demonstrates that she follows her parent's instructions and is accountable towards him. It is also emphasized that Juliet is very young. This is seen in her father's hesitation about discussing marriage.
When we compare this to the Juliet near the end of the play, there is a complete transformation. Juliet is very passionately in love with Romeo, which is demonstrated through her excitement on her wedding night. She is no longer an inexperienced child. Juliet is also no longer obedient towards her parents. Instead, she is willing to do anything in order to be with Romeo.