The top seems somewhat out of the norm for Buffy's character. I can't recall many other instances where she is wearing a short sleeve cardigan. The sunflower applique has more of a Willow vibe than a Buffy stylistic choice, in my opinion. None-the-less, it is a cute sweater.
Later, Buffy pulls off quite an impressive wardrobe change as she pulls up to the school wearing a pink camisole just to be be seen wearing a pair of high waist-ed slacks and a white tank in the very next scene.
Either Buffy pulled a Clark Kent and made a quick change in a phone booth or production made a small continuity error.