I am not saying you are wrong, art does depend on ones own preferences.
But one can still word it better.
Maybe I am too old already but 10-15y ago, your average 12year old gradeschooler was pretty much not able to even closely draw on this level.
Also, a comparison to a child's skill level is not nice, especially if it's pretty much an adult person with clearly better skills than an average child normally has. Doing that pretty much implies inexperience to a higher degree, which is not the case here. Sure there are better arts.
But a 12y old pretty much only starts to learn around that age more about art and how objects and the environment can truly be replicated. Their drawings will pretty much still be in a phase where they slowly give up their way of drawing schematically at that kinda age. Sure there may be some who can do it better, but there are also children who can go to university at the age of 14 or even 12 if not even younger nowadays. Still those are rather a minority. Clearly not as much as those early university kids, but in a way it's similar.
And this comment was sounding way more general than implying a case of a talented or diligent kid interested in art, that started drawing more seriously early on and had the ressources offered to it.
It's more rude than an opinion if you directly compare it to a 12y old childs work. I'd suggest better wording tbh... ╮( ̄▽ ̄)╭
That's why I made the distinction of talented and average children. I know there are talented kids in every possible subject including art like your sister being one but they are a minority and can never be used as a generalized comparison group like the original comment implied (probably unintentionally).
Your average 12year will is not able to draw for an anime, not to say draw a manga from scratch. But there still are twelve year olds better than most adults even but they are rather few than many. I don't need your proif though, I mean you see enough talenrs in the news ヾ(❀╹◡╹)ノ~
But help your sis realize her talents if you can. She sounds amazing and a talent as such is a gift only few can call their own. I hope she can make use of it and you support her well. (๑•ㅂ•)و✧
I don't want to sound mean but it looks like a 12 year old drew this