Michelle knew that she had gotten hit by the gun's beam, but she didn't know if anything had happened to her. She had already found out that people who got hit by the gun's beam thought that their new form was normal, so she had no idea who or what she was before.
Jon, her older brother, peeked his head out from behind his broken mirror. "Michelle? What happened? What was that light?" Jon no longer remembered Mikey, only his sister Michelle.
She definitely didn't want her brother to know about the transformation gun, so she lied and said she was trying out a new flashlight, to see if it worked. He bought it, and let her leave, after she grabbed the gun from his bedroom floor.