Princess Charlotte already outranks her uncle Prince Harry. She has since the day she was born.

He is fifth in line to the throne and she is third, and the gap opened on May 2, 2015, the day she arrived and went ahead of him immediately.
Two things about this get reported wrongly, and both of them matter.
The first is why he moved down, which was not because of his own children, since Archie and Lilibet came after him in the line, at sixth and seventh, and cannot displace him. He dropped because Prince George was born in 2013, Princess Charlotte in 2015 and Prince Louis in 2018, which are three children of his elder brother, all ahead of him.

The second is what happens next. If Prince William becomes King, Princess Charlotte moves to second in line behind her brother, but she does not become Princess of Wales, because that title belongs to the wife of the Prince of Wales and there is no version of the rules under which it passes to a sister. Prince George would in due course become Prince of Wales, while she would simply be Princess Charlotte, second in line.
The truly notable part is the legislation, since she holds her place because of the Succession to the Crown Act 2013, which ended male preference. Under the rules in force when her father was born, Prince Louis would have gone ahead of her the moment he arrived in 2018, and he did not, which makes her the first royal daughter protected that way.
She is eleven, at school in Berkshire, and by her father’s account she plays netball and does ballet, with no duties and no patronages, while sitting constitutionally two places ahead of an uncle who spent years as one of the family’s senior most working royals.