Well, she was nominated for grade 1 by two at the same level. She defeated a special grade curse without much difficulty. She almost knocked out a grade 2 with a rubber mallet. She fought against the Mahito clone, etc.
She has done more than Mai Mai, who needed her brother to kill a special grade cursed
Jesus Christ, let's do some BASIC scaling, shall we?
Ino states that Yuji's attack might be on Nanami's level, so let's say Nanami = Yuji (at least on AP)
How do we prove this? Simple, let's use Nobara, Ponytail guy humiliates her, but he's probably not too much stronger than her, so let's say Ponytail guy >=Nobara
Later, Nobara was fighting Mahitwo(Mahito's clone), and the two of then were comparable so Nobara=Mahitwo
Then we got
Nanami=Yuji
Ponytail guy>=Nobara=Mahitwo
SO, WHAT'S MY POINT? Ponytail says that if he weren't for his technique he would've died, wich means that Nanami can one-shot this guy
And in chapter 124, Yuji one-shots Mahitwo
Wich means that Ino's statemant about Yuji having a striking power similar to Nanami is proven true, and at the end of the day, Nobara would get one-shoted by both Yuji and Nanami, proving that Kugisaki is nowhere near 1 grade