This Year's Model of Humanity

I think she eventually realized that even though she's the Slayer, the "strongest one" out of them and the only one truly obligated to fight the fight, she needs them. After however many times of their saving her life as much as she's saved theirs, she came to see their individual value and how they contribute to the fight. Especially after Willow started getting really good with the magick and they both proved they weren't afraid to risk everything to help her -- not only that they weren't afraid, but that they succeeded so many times. There came a point when they all had each other's back, not just Buffy fighting and having to look after them all. She reverted back to it in The Yoko Factor and I think a couple other times, saying they would be in the way if she had to worry about protecting them, but in general she saw how important they were, and she got that the reason she's still around at all is because of them.