Before Dash and his sister fight at the dinner table in the beginning, the sister's hair is parted on the left side. Then, they fight, and the mom tries to stop them. Finally, when she does stop them, the sister's part is on the right side. This is when she has her head in her hands, you can see it clearly. Whoops!
No! Her hair is parted "parted" on the left side in the begining of the movie and all through the movie it switches sides. From a continuity point this is a slip up. BUT! I think they did it on purpose so you could see her face in several shots.
I've watched the scene and it is clearly a slip. Throughout the fight, her hair is covering her right eye, yet when Frozone and Mr Incredible leave, her hair is now covering her left eye!