Trying hard not to reveal my very young age, but my tween years was filled with early 2000's girl power slogans:
My all time favorite was the Powerpuff Girls (the ORIGINAL, of course!). This song is part of the show's tween-pop CD released in early 2000.
A particular episode screams "post-feminism": The episode "Equality Fights"
In this episode, the Powerpuff Girls meet a villain, Female Fatale, who robs banks to teach the patriarchy a lesson. At first, the Girls are swept by the villain's message of mistreatment by men. By the end of the episode, the girls greet the villain by telling her about famous women (the traditional white feminist icons ie Susan B. Anthony and the like) who didn't hate men, and then throw her in jail. It's really telling that the series is created by a man, Craig McCrakken, and his future wife, Laura Faust, who proudly proclaims her feminist intent in her show, My Little Pony: Friendship is Magic. It's also really telling that girls collaborate with police, noting how white feminism typically colludes with structures of white supremacy such as policing.
Another movie set I enjoyed as a tween was the Cheetah Girls, also featuring girl power songs. I remember loving the song "Cinderella" because it was, really, the first song that was bluntly post-feminist to me: