In Speak, by Laurie Halse Anderson, what does Melinda do to the mirror?

After she undergoes a traumatic rape during her first high school party, Melinda does not report the incident to anyone. However, her silence only causes her distress and mental turmoil. Her situation is worsened by the isolation she experiences from her busy parents and judgmental friends.
She hates herself for what happened and cannot stand to look at her reflection because she thinks she is ugly. Therefore, Melinda avoids mirrors at all cost. At home, she hides her mirror at the back of her bedroom closet. In the broom closet where Melinda seeks refuge while at school, she covers the mirror with a Maya Angelou poster the librarian had given her. The only mirror she seems to have tolerated is the three-way mirror at Effert’s, which she equally manipulates to distort her reflection in order to resemble one of Picasso’s sketches.

Mirrors are a constant symbol in Speak. Melinda hates mirrors because they remind her of what she perceives to be her ugliness. She hates them so much that she actually covers them up. She literally cannot look herself in the eye. Mirrors reflect the way that the world sees Melissa, a highly negative image she increasingly internalizes.
Towards the end of the story, however, the mirror comes to take on a completely different significance. Andy tries once again to rape Melinda. It was his violation of her the previous summer that precipitated the immense psychological turmoil that she's been suffering ever since. But this time she resists. Melinda's always hated herself for what she perceives to have been her weakness in not preventing Andy from raping her. Now, however, she smashes her closet mirror and uses a shard of broken glass to threaten Andy.
This time, Andy backs off. For Melinda mirrors are no longer a symbol of poor body image and lack of self-esteem; they represent a sense of empowerment and control, a means of fighting back against a cruel world and establishing herself as someone to be valued and respected: someone that was there in the mirror all along.