Princess Charlotte is the first young royal girl who will benefit from a massive change to the line of succession, which makes her more likely to be Queen than her great-aunt Princess Anne ever was

For most of royal history, any male children who were born into the House of Windsor were prioritised in the line of succession over their female counterparts. However, when Prince William and Princess Kate were expecting their first child, the whole system was overhauled which meant female and male children were on an equal footing.
Previously, even if a baby girl had been born first, any male children that followed would have overtaken them in the line of succession – meaning that the country was always far more likely to have a King as monarch than a Queen. However, during the late Queen’s reign this changed forever.
During Princess Kate’s first pregnancy a new piece of legislation was created meant that whether her first child had been a boy or a girl they would have remained the heir to the throne no matter what – changing to absolute primogeniture from male primogeniture.

The Act of Succession (2013) also removed “provisions by which those who marry Roman Catholics are disqualified from the line of succession. The changes came into force in all sixteen Realms in March 2015,” – per the Royal Family’s official website.