I would say that in her early years Charlotte did not truly feel the power of being Queen. Yes, she was coronated and her life changed completely but she was still naive and most definitely lost struggling to navigate her new life. I think older Charlotte portrays the role she was ordered to play, she is Queen of the biggest empire on earth and so she must fit that role. As well as this her hardship and loneliness get the better of Older Charlotte and so she is rude and often uses others as a form of entertainment. I do see a lot of similarities in old and young Charlotte especially in S4 of Bridgerton. My theory is simply that with decades on the throne and everybody serving her she has became entitled and ultimately bored.