Responses
She has no interest in Setsu's own sound. She wanted a winner, she wanted him on that stage as "Matsugorou's grandson" NOT as "Sawamura Setsu".
The father is no better. They clearly are two people in pursuit of "greater music"; Umeko in wanting to create a Matsugorou 2.0 and the father who likely had a son with her to sire an heir with the blood of two shamisen masters...
TL;DR: So yes, thank God for Wakana...
Nothing from Umeko's actions, expressions and body language ever lead me to believe that she is a good mother... Perhaps she herself believes she is paving a way for her son's musical growth, but in the end it is nothing more than a clear obsession towards a dead man's music ..
She sees Setsu as nothing more than an extension of his grandfather, given her insistence in having her son play to Matsugorou's sound.
Her clear distaste towards the sound Setsu wanted to convey was an indication of that. Her dropping the trophy onstage was a rejection of Setsu's music, as well as an act of humiliation. She may brush that off as something she did to "motivate" her son but that very action is nothing short of damaging (let's keep in mind that he's only 16....).