Look at 1:29. Correct me if I'm wrong, but she clearly uses her sharingan to break the genjutsu. She doesn't just "see which flag is the true one" she literally disables all the other ones.
That's exactly what I said, she uses her Sharingan to find the real one, and she uses "Kai" to release the Genjutsu all together.
There's no such thing as releasing a Genjutsu with another Genjutsu. There is a Sharingan technique at 3rd Tomoe that does reverse a Genjutsu used on another (what Itachi did to that one chick who was Team 8's leader, forgot her name lmao)