The story does not tell us how Margot will act after she emerges from the closet. However, we can probably make some speculations about her likely actions after she is let out.
First, Margot is likely to be very angry. After all, the sun only comes out once every seven years in Venus. We know that Margot, more than any of the other children, has been looking forward to seeing the sun.
The text tells us that Margot desperately tried to dissuade the children from their cruel errand. We also learn that she threw herself against the door and beat on it after she was locked in. So, Margot is likely to be very angry after she is let out.
Second, although it is possible to guess Margot's emotional condition, it is difficult to predict Margot's likely actions upon emerging from the closet. Her anger may remain dormant or even hidden from the children. From the text, we learn that Margot is naturally introverted and that she is habitually wary during her interactions with the other children. She often says very little, even when her patience has been sorely tested.
When William pushes her, she does not push back. Even when the children accuse her of lying about her experiences with the sun, Margot remains characteristically silent.
However, Margot does occasionally have emotional outbursts; the text tells us that she once refused to take a shower at school and that she screamed at the thought of water touching her head. So, at this point, we can speculate about Margot's emotions after emerging from the closet. However, it may be a little harder to predict how she will act out her anger.