all the flashbacks have made it kinda difficult to trace the sequence of events in this series, so I reread from the beginning really attentively and I think I have the timeline pieced together, in case I'm not the only one confused.
Aikawa loses her desire to play music at her previous school after receiving harsh criticism and being told not to play the way she enjoys.
Aikawa transfers into the current school, while her mother? reminds her that she is expected to continue music, (with the gifted silver polishing cloth for the silver trumpet she was told to use, even though she loves the sound of gold trumpets).
Aikawa heard Katagiri practicing on the roof and decides to get close to her to try to rediscover her love of music, and she seemingly does, beating Katagiri in the audition and being overjoyed that Katagiri wants to play with her even after losing the audition. But the band director or w/e recommends that she quits, which seems like its going to lead into the present day events, where Aikawa is dating the boy "until the competition" where she will presumably quit taking music seriously.
Best guess at this point is she's trying to distance herself from Katagiri in preparation for leaving the brass band?