Hooray!!! A Short Piece!!
Yeah, the piece is short, but has some good content. We clearly begin in G major with scalar passages and jumps within the tonic triad. Within this symmetrical and parallel double period are sprinkled a half cadence (m. 8), a PAC (m. 16). To spice things up a big, Bach decides to take us for a stroll in the dominant key of D Major in measure 17. (the c sharp is the determining factor) Measures 23-24 are our authentic cadence for the D Major B section. Our c natural in measure 24 takes us ever-so-smoothly back to our friend G major for measure 25 through the end. We finish off with an expected G Major chord to finish off our round of perfect authentic cadences.
Nice job, Bach. I'm sure Anna was pleased.