Warning: this post is entirely spoilers for Buffy Season 7.
One of the wonderful things about Buffy is her awareness of power dynamics. This is most explicit in Checkpoint (5.17), when she discovers that both the Watcher’s Council and Glory, the Hell-Goddess, are behaving as if she is powerless in an attempt to undermine her power. She reclaims her power, and in the process completely redefines the playing field. However, it is most resonant in Choices (7.22). The name of the episode itself conveys so much: for seven years, we (and Buffy) have been told that she is “the Chosen One”, the one girl in all the world to fight the demons and the forces of darkness. Only a few episodes earlier we had discovered that the power was forced into the First Slayer by the first Watchers, in an act some have likened to metaphysical rape, and that the only help those Watchers could provide was to give Buffy another dose of that essentially-demonic power. Instead, Buffy redefines not only the field, but the entire game. She gives the girls themselves, all the Potential Slayers she has gathered, the choice to take up the power and “be strong”. She takes them from passive creatures to active agents, from “We the Watchers have chosen you to be the Slayer” to “I chose to be a Slayer.”
This is beautifully foreshadowed an episode earlier in the season, Same Time, Same Place (7.3).
Buffy has long made the conscious choice to be The Slayer. She first actively chooses it at the end of the first season, when she knows of her prophesied death and goes to do her duty anyway. At least once a season after that, she has to reaffirm her decision to put her life on the line for the greater good. In the end, she offers the ultimate Choice to the Potentials, and by proxy all women, and thereby empowers herself and all of them/us. No longer is there a Chosen One, and Buffy is free to make her own choices in life.