The Spiral of Silence Theory suggests that the more an individual feels their opinion is different
from the majority opinion, the more likely they are willing to voice their thoughts in the public discourse. A lot of people remain silent when they feel that their opinion or views on a certain subject is in opposition to the views of others, and that most people tend to gravitate to the mass opinion view.
This scene is a good example of the Spiral of Silence Theory. Cady decides to not say anything about her friend being removed from the table because she still wants to be apart of the group. You can see how her opinion differs from the other girls based on her expression and face, but since the other girls in the group have a certain opinion, she can't go against it because she knows they will remove her from the table as well.