Megan is a survivor of the waves and was one of the children brought to Camp Haven. She was implanted with an alien explosive in her throat that turned her into a living bomb. According to the books, she is a very thin girl who wears a Hello Kitty shirt.
She ends up surviving the 5th Wave and now lives in the care of Ben and Ringer alongside Sam and baby Cassie.
Megan is a little girl who was in a school bus with Sam Sullivan when they arrived at Camp Haven. She was not marked as a 'Red' and was supposedly carted off to the hospital. When her and Sammy split ways coming off the bus, he was very apprehensive about leaving her because she was kicking and screaming.
She appears in "The Infinite Sea," and is rigged with an explosive device lodged in her throat that detects carbon dioxide used to kill survivors. Evan and Cassie were then able to successfully defuse the bomb implanted inside Megan's throat and save not only Megan herself, but the other survivors. The bomb implanted in her is later used by Poundcake to kill Grace (killing himself in the process).
Megan stayed with the others when they went to hold up in Grace's safehouse. She began to keep Bear around her and began to call it 'Captain'. Sam, angry and annoyed that she was keeping it around her, said that Bear was his name. She would argue back that Bear was what he was and wasn't a real name. She kept calling it Captain even more to annoy him.