My (pre-grade one) daughter's latest piano piece is in D minor but in the middle it modulates into something else for a few bars, although the key signature doesn't change. It is in 2/4, and in the modulation bar 1= minim G#, bar 2= dotted crotchet F#, quaver E#, bar 3 = quaver F#, quaver A, crotchet F natural tied to a crotchet F natural in the following bar with a crotchet rest. (Both hands are playing in unison in the modulation so there is no harmony). The whole thing is repeated and then it goes back to D minor (with both hands doing separate things).
My daughter is unfazed by the E# but wants to know why what could have been a second E# is written as an F natural instead. Any suggestions?