Squirrel Killer is right on the money. If she had been male, she would be fourth in line to the throne. As the only daughter of the monarch, all of her male siblings and all of their respective children are ahead of her in the line of succession.
She’s behind them (at 9) because the girls are only children of the second and third sons of the queen (5,6,8). Her children come up last in the grand-child succession order simply because Anne is the only daughter.
If Andrew had a son, that son would leap ahead of his daughters in the order of succession.
It’s not rocket science. Daughters can and do inherit. But it all depends on having no brothers or no children of brothers hanging around.
Not that it matters all that much. Once you get down to 4th or 5th on the list, you need a War of the Roses or King Ralph situation to have anything happen in your favor.
Not quite through first born son, but it does follow first born.
If First born snuffs it then his/her offspring are next in line. If there aren’t any, for whatever reason, then it passes to next born offspring of monarch and then to their offspring and so on. After relevant siblings and their offspring are exhausted it gets a bit convoluted and I don’t pretend to understand where it goes from there (though I assume it would pass to the Queen’s Sister).
I presume that if one Charles’ kids has a sprog before he gets to the throne then the line of succession would pass through them before it gets to any of Charles’ siblings.