Honestly that's what i was also thinking when i read the recent chapter, i agree with you.
Tbh I don't think it's her fault but the opera singer whether good or bad it wouldn't have mattered. People are always looking forward to the new trends and will always favor things that left even the smallest impression out of curiosity. The girl was a teen or child yes but they are competing on even grounds at this point. The only advantage Lippe has is that she's mature. She didn't really practicing singing before because she was scared.
Although I do agree it was unnecessary for Lippe to commit fatality against the girl. Even if she is mature she didn't care about the girl in the slightest anyway. It's not like she went out of her way to sabotage her. The author could've made her perform well as well but i would understand her nerves after hearing something so drastically different. Lippe performed to change people's minds about folk songs and it just so happened that some other girl wanted to make it a competition to which she didn't care about.
Did they really have to make the opera singer bad just to prove that Lippy is good? Couldn’t Lippy have just shocked and awed these people without the author having to drive home how awesome she is by sabotaging every other character, especially someone who is apparently a professional singer.
Also,I kinda feel off with all these minor villains being literal children. Like, it’s kinda hard to go “haha villain! You deserved this because you were rude to our protagonist!” When the villain is like… 12 years old. It feels like laughing at a crying child. We have a major villain and the murder of her family to focus on, do we really need to be wasting our time seeing how Lippy beats other children, especially because Lippy is an adult herself. Are we meant tot cheer that an adult is more mature and well mannered than a teenager?
What I’m trying to say is, I just wish they could show us how cool Lippy is without having to dumb down every other character. I can’t really cheer for an adult defeating a child. Everyone could have been amazed at Lippy’s singing without the author ruining another characters abilities. Making that character mean for all of two seconds and then embarrassing them literally adds nothing to the story. It’s just taking time away from our main characters and quests.